Make paint selector layout constant
Closes #1510 (closed)
See the issue for images of how the status bar layout changes depending on how object properties are displayed in the paint selector.
To do this, the MR has to
- introduce constant sizes for all of the elements contained: a/m flag, paint preview, stroke width
- move the elements into their own table cells rather all in the same box
With some design suggestions from @adam.belis