The new approach enables the parser as soon the Tests navigation
widget or the Tests results pane is visible.
If none is displayed parsing will be disabled.

This additionally fixes an issue of not parsing a project
when having a project opened already before triggering the
first Tests navigation widget to become visible.

Change-Id: I7163268d405e07e85814097d65ff34790a98a3d1
Reviewed-by: Andre Poenitz <andre.poenitz@theqtcompany.com>