ControllerFacade::deselectAllAndSelectFaces must return a value.

Signed-off-by: Kristian Duske <kristian.duske@gmail.com>
Add a few utility methods for dealing with dropped files.

Signed-off-by: Kristian Duske <kristian.duske@gmail.com>
Limit file dropping to the texture collection editor and entity definition file chooser to avoid conflicts with entity dnd.

Signed-off-by: Kristian Duske <kristian.duske@gmail.com>