Make vcs segments *much* faster

Do not call vcs status unless the relevant files have changed.
Uses inotify, if available, otherwise falls back to stat() based
monitoring. Fixes #396
Move --config and --theme_option processing to finish_args
Use deepcopy in powerline.lib.config
Fix tmux cwd segment

Fixes #467

Still needs colors for cwd:current_folder, cwd and cwd:divider
Fix tmux tests
Also fix bash tests
Remove debugging lines
Fix tests failing if inotify not available
Forgot to move the import to module level
Turn off status colors by default in vim as well
Add a debug() function to allow command line debugging of the vcs code
Merge remote-tracking branch 'kovidgoyal/vcs' into develop
Merge remote-tracking branch 'zyx-i/powerline-daemon' into develop