UI scaling improvements

[lilyCalla]

Fix general UI scaling bugs including

• Top bar elements drift downwards when scale goes under 1.0
• Background for "Actions" bar didn't automatically adjust to rescaled sizing (required second click on "Actions" menu item)
• Prevent BPM "ratchet" issues where scaling up increases keypad button height, but scaling down leaves it at the maximum height scaled to
• Beat Indicator / Stop all button not scaling with UI
• interface jitter in UI Setting editor
• Width of text elements in UI settings editor, but font size changes
• Undo/Redo buttons to layout to scale properly
• Prevent text overflow in about dialog

Current (Beat generator panel has been scaled up, then returned to smaller size):

Pull Request:

[mcallegari]

Are you sure this syntax makes sense?

[lilyCalla]

This syntax is meant to prevent a binding from being created on origItemHeight. To my knowledge this is the cleanest way to do this inline, although I'm open to being wrong

[mcallegari]

TBH I've never seen that syntax before.
I'll merge this as it is. Thanks

[mcallegari]

Hey, thanks for this.
Just 2 comments but the rest looks fine to me.

[coveralls]

coverage: 32.074% (-0.007%) from 32.081%
when pulling cbd5487 on lilyCalla:ui-scaling-improvement
into 8e695ef on mcallegari:master.