Enable Context Help (Shift+F1) using "QT's - What's This"

... adds "What's this" to (hopefully) most of the widgets (please report
on missing ones)
... defines draft "Whats' this" texts including a
context specific WikiLink

.. Help Key for all platforms is <Shift>+<F1> + in some widgets
"RightMouse - Click"

... Tested on Win and Mac (On Mac QtMacButton seems not supporting
"What's this") - so here <Shift>+<F1> has no result.

... ToDo: Create final texts and links based on the to be updated 3.11
Wiki
Merge pull request #1200 from Joern-R/help2

Enable Context Help (Shift+F1) using "QT's - What's This"