35846 code polish

[sgsteph]

Addressed most of pending code review comments

• Revisited Project chooser screen navigation
• Added the ability to discard thumbnail downloading
• Added dedicated signals / slots for dropped EDL / Movie
• Allowed EDL and movie to be dropped together
• Removed some CutSummary setters and set needed values in init

[raphaelmatto]

Code looks great! Lets get this merged to master.