update .gitignore for docs and pycharm
TST: shorten long running test
Small fixes in manual tests
Add possibility to specify dataframe and aes per geom

This makes it possible to specify `geom(data=df, aes=aes(...))`. This
needed a bigger refactoring for the methods which manipulated the
underlying data.

Also adds a basic tests for this functionality.
Merge pull request #124 from JanSchulz/geom-data

Geom data