FFE request - [composer] Add view menu option to hide bounding boxes

I'm requesting a feature freeze exemption to get this feature into 2.6. What it does is add an option in the view menu for compositions to hide the bounding boxes of the currently selected feature. It's a standard feature in design programs as it allows you to tweak the size and position of items and see exactly what the result is without the bounding boxes / mouse resize handles getting in the way.

Reasons for an exemption:
- the code is self contained, it has no impact on any other code areas, so it's very low risk
- I know this part of the code base backwards - these changes don't introduce any regressions
- it's a really handy feature to have and it's ready to go