Remove python-mode plugin.

It is not working well anymore. Might be incompatible with
YouCompleteMe or it just sucks.
Use Syntastic code checking for python.
Reenable YouCompleteMe for Python completion.
Load ropevim if available.
Vundle update.
Syntastic settings.
ropevim for OS X.
Add function to load Python virtualenvs.
Set PYTHONPATH on loading virtualenv.