Make the Greeter's help window resolution-aware
Currently it’s set to a static 800x600, so it probably doesn’t work well for lower resolutions, and makes poor use of the screen estate of larger ones.
We should make the help window aware of the screen resolution and make it determine its size depending on it.
Related issues
- Related to #7880 (closed)
Original created by @anonym on 7009 (Redmine)