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]

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 cbd54876445a7031b5c2e02ec6f51277d3a4791e on lilyCalla:ui-scaling-improvement into 8e695ef306f1a0d81a78099bff0de0b6a53ac0d0 on mcallegari:master.