Fix #24 Faces were painted before the image. Moreover, if the face does not have a valid color, it takes the background color for the brush. We just had transparency, and the image thus stays visible behind the faces.
Minor ui improvements
Merge branch 'feature/task-version_1.2-CGAL_Arrangement' of https://github.com/oliviertournaire/QLabelling into feature/task-version_1.2-CGAL_Arrangement
remove useless actions in ui
restore verticesPen before drawing them
#23 Change current implementation to warn the user if no image is open. Editing tools are not enabled until an image is opened
#23 Fix warning message if no image has been loaded