Add general completers support
Add general UltiSnips snippet completer
Add general filename completer & other stuff
Rewriting the code from the pull request

This implements the filename completer and introduces integration with
UltiSnips. The user will now see snippets in the completion menu. After
selecting a snippet, the user should invoke the UltiSnips trigger key
(which should be changed from the default of TAB) to trigger the snippet
expansion.

Fixes #77, Fixes #36
User can now pick the root for relative paths
Filename completer now uses threads

This was done by introducing a new ThreadedCompleter class that descends from
Completer. Both JediCompleter and FilenameCompleter descend from
ThreadedCompleter.
Merge branch 'JazzCore-general_completers'

Conflicts:
	python/ycm.py