Fix unlabelled sliders in Mouse & Touchpad (LP: #1569227)
The problem was that the labels existed but had been clipped to zero height in ItemTitle.qml, so never appeared. However once you make them appear they conflict visually with the things around them (also fixed here).
Also: * improved the title texts * increased the visibility of the main Mouse and Touchpad titles * removed the clumsy misplaced "Slow" and "Fast" labels * added comments describing what needs fixing next (in SliderMenu which is a different project) to replace the old Slow and Fast labels
System Settings needs A LOT of visual fixes so I had to restrain myself and tried to keep this change mostly about just fixing LP: #1569227. (LP: #1569227)