BUG: Restore return value in notebook reprs
Monkey patches the _ipython_display_ method onto NDFrame, so that
notebook cells have a real return value. Setting the
display.html.table_schema will monkey patch the method on,
and remove it when unset.

closes https://github.com/ipython/ipython/issues/10491
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=h1) Report
> Merging [#16171](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/a7a0574a0bcb8a4c65ed7f5006972e24f90ae3df?src=pr&el=desc) will **increase** coverage by `0.02%`.
> The diff coverage is `85%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16171/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16171      +/-   ##
==========================================
+ Coverage   90.86%   90.88%   +0.02%     
==========================================
  Files         162      162              
  Lines       50819    50826       +7     
==========================================
+ Hits        46177    46195      +18     
+ Misses       4642     4631      -11
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.67% <85%> (+0.02%)` | :arrow_up: |
| #single | `40.32% <15%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `91.67% <ø> (+0.03%)` | :arrow_up: |
| [pandas/core/config\_init.py](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29uZmlnX2luaXQucHk=) | `93.86% <85%> (-0.43%)` | :arrow_down: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `90.68% <0%> (-0.35%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.35% <0%> (+1.81%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=footer). Last update [a7a0574...c70de54](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=h1) Report
> Merging [#16171](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/a7a0574a0bcb8a4c65ed7f5006972e24f90ae3df?src=pr&el=desc) will **increase** coverage by `0.02%`.
> The diff coverage is `90.9%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16171/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16171      +/-   ##
==========================================
+ Coverage   90.86%   90.88%   +0.02%     
==========================================
  Files         162      162              
  Lines       50819    50827       +8     
==========================================
+ Hits        46177    46195      +18     
+ Misses       4642     4632      -10
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.66% <90.9%> (+0.02%)` | :arrow_up: |
| #single | `40.33% <13.63%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/config\_init.py](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29uZmlnX2luaXQucHk=) | `94.52% <100%> (+0.23%)` | :arrow_up: |
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `91.63% <87.5%> (ø)` | :arrow_up: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `90.68% <0%> (-0.35%)` | :arrow_down: |
| [pandas/compat/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9fX2luaXRfXy5weQ==) | `62.22% <0%> (-0.11%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.35% <0%> (+1.81%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=footer). Last update [a7a0574...fd24e27](https://codecov.io/gh/pandas-dev/pandas/pull/16171?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @jreback look ok to you? yep