Inconsistent indexes for tick label plotting
The tick position for BarPlot can be define using the convert tool from matplotlib.

The main advantage is that it will reuse the same position when you have text as axis values. Previously, the tick position was determined by the order of the given element, so that ['A', 'B'] where given label [0, 1], and if updating the plot with order ['B', 'A'], you will not draw at the right position.
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The resulting plot for each issue would be:
![issue26186](https://user-images.githubusercontent.com/49879400/65983815-b24e5100-e47e-11e9-87c5-8c536744da28.png)
![issue11465](https://user-images.githubusercontent.com/49879400/65983825-b8443200-e47e-11e9-954d-76919e96c38f.png)
- [x] closes #26186
- [x] closes #11465
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

So one of the example of the doc revealed a bug in this PR. 
I added it to the test suite and hopefully will fix it. It is about using a MultiIndex of string (or containing a string in a level?) as axis label. This PR solved the bug related to index, but handling MultiIndex in the same way requires more work and I consider it outside the scope of this PR, so I expressely did not handle it.

The best way to handle MultiIndex plot would be via label grouping and multi-level axis label, as described in this issue on matplotlib matplotlib/matplotlib#6321, and this one on pandas #2088. I may try to tackle this one day, but definitly not in this PR.
 can you merge master and will look again I made the dtype for tick array as int as pointed by @WillAyd, see last commit change.
I also rebased on master. @nrebena I think this should be good. Can you fix the merge conflict? Rebased and green :green_apple:  @WillAyd  Hi @nrebena - sorry to chase you up, just wanted to ask if this is still active Hi. No worries. I may come around to finish it, but if someone want to take it over no problem.  Rebased on master and correction done. @jreback I improve the warning behavior to warn about REdrawing a bar plot with a MultiIndex, and add comment in the test to make it more explicit what is does. can u merge master and resolve issues and will look @nrebena can you move release note to 1.2 and merge upstream/master to resolve conflict > @nrebena can you move release note to 1.2 and merge upstream/master to resolve conflict

Hi @nrebena - could you address Simon's comment if this is still active? It looks like it's pretty close to being ready @nrebena can you merge master once more?

ping @jreback  thanks @nrebena , very nice PR!

thanks @MarcoGorelli for resolving the conflicts! this PR was reverted, but I guess we don't have a tracking issue. @nrebena can you open one.