vim: external utilities, python mode.

Add custom python ftplugin as I'm going to be doing a lot of python programming.
It includes utilities for making & error jumping, for pasting to ipython,
navigating functions and classes, opening help and notes, etc.

Also define some general utility functions that are used by ftplugins and
constitute the interface with my desktop tools:

  Open() -> xdg-open
  Search() -> search
  Launch() -> launch
  Browse() -> launch browser
search: fix quotation bug.