Sketcher: Correct font sizes and updates

========================================

Fonts:
- SoDatumLabel internally uses QFont and thus points. It was being fed pixels, for which the configured size in preferences did not match the actual on screen size. This is corrected.
- Font sizes fed directly from parameters to the coin nodes skeleton were not being updated, as the parameter observer is initialised after the nodes are created, and the parameter
observer was not configured to update this nodes. This is corrected.

Colors:
- Some color parameters were not being being updated by the parameter observer. This is corrected.

src/Mod/Sketcher/Gui/EditModeCoinManagerParameters.cpp

@@ -51,5 +51,6 @@ SbColor DrawingParameters::ConstrIcoColor                           (1.0f,  0.14
 SbColor DrawingParameters::NonDrivingConstrDimColor                 (0.0f,  0.149f, 1.0f);   // #0026FF -> (  0, 38,255)
 SbColor DrawingParameters::ExprBasedConstrDimColor                  (1.0f,  0.5f,   0.149f);   // #FF7F26 -> (255, 127,38)
 SbColor DrawingParameters::DeactivatedConstrDimColor                (0.8f,  0.8f,   0.8f);     // #CCCCCC -> (204,204,204)
+SbColor DrawingParameters::CursorTextColor                          (0.0f,  0.0f,   1.0f);  // #0000FF -> (0,0,255)
 
 const MultiFieldId MultiFieldId::Invalid = MultiFieldId();