BUG: Make Styler ignore None index names to match to_html behaviour
Addresses https://github.com/pydata/pandas/pull/12090#issuecomment-180695902 by making the `Styler` behaviour match regular `to_html` behaviour. 

This PR is based from #12162.
##### New behaviour

<img width="596" alt="screen shot 2016-02-08 at 10 35 23 am" src="https://cloud.githubusercontent.com/assets/3064019/12890011/b183e81e-ce4f-11e5-9b9f-c021fcb33c5a.png">

cc @TomAugspurger 

Actual commit: https://github.com/pydata/pandas/commit/0cb2be1cd94483057b59bc714b0a73a7bfe27b77
 Tests are failing on lint with files this PR doesn't touch: https://travis-ci.org/pydata/pandas/jobs/107799224#L1134-L1154

```
$ ci/lint.sh
inside ci/lint.sh
discarding /home/travis/miniconda/bin from PATH
prepending /home/travis/miniconda/envs/pandas/bin to PATH
linting -> pandas/core
linting -> pandas/io
pandas/io/sql.py:24:1: F401 'Appender' imported but unused
pandas/io/tests/test_sql.py:2327:33: E127 continuation line over-indented for visual indent
pandas/io/tests/test_sql.py:2675:33: E127 continuation line over-indented for visual indent
pandas/io/tests/test_sql.py:2741:25: E127 continuation line over-indented for visual indent
linting -> pandas/stats
linting -> pandas/compat
linting -> pandas/sparse
linting -> pandas/tools
linting -> pandas/tseries
linting -> pandas/tests
linting -> pandas/computation
linting -> pandas/util
The command "ci/lint.sh" exited with 1.
```
 Joris is fixing that [here](https://github.com/pydata/pandas/pull/12263). I'll restart your travis build once that's merged.
 @HHammond can you rebase on master when you get a chance. I _think_ it should be a clean rebase.
 @jreback Wanted to double check with you before I mess anything up, the merge script will handle this merge cleanly right? There's the two commits, one of which is now in master. Second commit has no conflicts.
 you can run the merge script then pause when it asked if u want to push upstream
thrn in another window check that everything is good (you can even edit the commit message at this point)
 OK, thanks. I'll document that in the wiki.
 For some reason, the travis builds started to fail after merging this one. But does not seem to be related at first sight ("ImportError: libgfortran.so.1: cannot open shared object file: No such file or directory" and "ERROR: test_get_all_data (pandas.io.tests.test_data.TestYahooOptions)")
 Looking into it now, sorry.
