New (native) commit window

This is based on the previous commit window code base. It replaces the
NSTextView with a OakTextView for entering the commit message to take advantage
of the git grammar features. E.g., fixup!.

If other SCM bundles are updated in the future to include any specific grammars,
these can be used in the commit window by setting the bundle grammar to
"text.SCM-commit", where SCM could be hg or svn for example.

One change to note is that the row button "Modify" for the "--action-cmd" commands
are now implemented in the action menu. If commands are not available for the
selected file, the menu items will be disabled. The action menu is also available
as a contextual menu.

TODO
  * Add history for previous commits
  * Resize tableView based on number of files (cap at 10)
Export TM_SCM_NAME variable

We use this to set the appropiate grammar when launching the commit window.