optimisation and message dialog

Message dialog for create selection sets. User gets warning that this
could take a while and has now the choice to abort this action.
Creation of selection sets fixed and more robust

Changed the creation of the selection sets.
Now the uv values are evaluated via the polygon and not the vertices.
This makes sure that only the poly in a specific quadrant is selected.
The previous method via vertex lead to double selection sometimes. So
polys in other quadrants could end up in different selection sets.
This is now fixed and the progress bar works now as well.
Merge pull request #1 from nicelifeBS/v1.4

V1.4