UI|Client|GuiRootWidget: Slightly thinner widget background frame
Fixed|qmake|Client: Typo in convenience header file names
UI|Client|GuiWidget: Tracking button clicks of any mouse button

Not hardcoded to the Left button.
Fixed|UI|Client: Initial viewResized event to mewly added children

Hitherto widgets have received a viewResized event only when the
actual Canvas size has changed. This has only accidentally worked
correctly because most widgets are present before the window is
ready for GL drawing.

Now widgets get sent viewResized whenever they become part of the
widget tree.