CLN: Add axis kwarg to Series wrapper for compat

Update tests to cover full range of Series flex ops and check that they
all accept an axis argument.
Merge pull request #5352 from jtratner/add-axis-kwarg-to-series-flex

CLN: Add axis kwarg to Series wrapper for compat
BUG/ENH: Allow drop to accept axis name

Add tests for DataFrame, Series and Panel, with axis checks, etc.