[516248] Actions for previous/next unresolved change

Introduce new actions for selecting the previous or next unresolved
change in a comparison:
- Add compare configuration property to hide/show new actions.
- Refactor diff selection actions into single class.
- Add key bindings for new actions.

Includes tests.

Bug: 516248
Change-Id: Idb572292ed84867d40cce5cb5491a4c8d76caa36
Also-by: Tobias Ortmayr <tortmayr.ext@eclipsesource.com>
Signed-off-by: Martin Fleck <mfleck@eclipsesource.com>
12 files changed