git-cola: avoid symbol conflicts

Rename 'cmds' to 'subparser' so that we can import the `cmds` module.

Signed-off-by: David Aguilar <davvid@gmail.com>
diff: remove `self.mode` state

We already have a reference to the model so it's simpler to just check
at runtime instead of storing state and using a callback to update it.

Signed-off-by: David Aguilar <davvid@gmail.com>
git-cola: add --amend command-line flag

Make `git-cola --amend` starts git-cola in amend mode.

Closes #187

Suggested-by: Nicolas Dietrich <nicodietrich@gmail.com>
Signed-off-by: David Aguilar <davvid@gmail.com>
git-cola v1.9.3

Signed-off-by: David Aguilar <davvid@gmail.com>