Add projectile-vc-dir bound to C-c p v

Define new function projectile-vc-dir which runs vc-dir on the project's root directory.  Bind this to C-c p v by default.
Add C-c p v (projectile-vc-dir) to Keybinding summary
Add occur mode to globally ignored projectile modes.

When using multi-occur (C-c p o) multiple times with the same regex, it lists
all the matches in the opened occur buffers. Adding the occur-mode to the
ignored modes stops this.
Merge pull request #202 from maxsz/master

Add occur mode to globally ignored projectile modes.
Merge pull request #198 from nwidger/master

Add projectile-vc-dir bound to C-c p v