Selecting vertical/horizontal/grid containers within a vertical/horizontal/grid container should draw a box when selected

[Wumpf]

In the above scenario I'd expect a blue box around both space views in the vertical container since it was selected (and a grey one on hover, in accordance with out highlighting colors).

(this screenshot is lacking selection here, this should ofc only show when still selected)

This would help localizing where's what in the viewport.

[emilk]

First step:

• Make object hover & selection colors brighter and more pronounced #6596