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

src/MergeActivityWizard.cpp

@@ -21,6 +21,7 @@
 #include "Context.h"
 #include "RideCache.h"
 #include "MainWindow.h"
+#include "HelpWhatsThis.h"
 
 // minimum R-squared fit when trying to find offsets to
 // merge ride files. Lower numbers mean happier to take
@@ -60,6 +61,9 @@ MergeActivityWizard::MergeActivityWizard(Context *context) : QWizard(context->ma
 #endif
     setWindowTitle(tr("Combine Activities"));
 
+    HelpWhatsThis *help = new HelpWhatsThis(this);
+    this->setWhatsThis(help->getWhatsThisText(HelpWhatsThis::MenuBar_Activity_CombineRides));
+
     setFixedHeight(530);
     setFixedWidth(550);