Make sure you can't paste rubric too close to scorebox

Some fixes for the forbidden area around the score box.

• Fixes #1264 (closed)
• Adds a bit more space around the scorebox so that you can't paste immediately around it
• Adds more forbidden space to right of the scorebox so that things aren't obscured when score updated (and box widens)
• check the ghost-text's bounding box for intersection with the forbidden area (#1264 (closed))

Needs

• light review
• light test

and merging.