Fix Tab Order on New Branch dialog to include "Create" and "Cancel" buttons.

[deckblad]

Current behavior:

1. Right click a commit, click "Create Branch"
2. Cursor is now focused on Name field
3. Type a name
4. Hit Tab
5. Cursor is now focused on "Check Out:" checkbox
6. Hit Space, checkbox is now checked.
7. Hit Tab
8. Cursor is now focused outside of pop-up dialog.
9. Hit Space, extension sidebar collapses.

I'd love it if the tab order on that pop-up dialog could be set so it continues to the "Create Branch" and "Cancel" buttons after the "Check Out:" checkbox.

Thanks!