Update branding and splashscreen

[aymanhab]

4.5 -> 4.6
List of contributors
icons for dialogs (framex.gif) 3 sizes
Update About panel with sponsors if needed
Possibly update installer icon

[aymanhab]

Splash is done, thanks @mattpetrucci
About panel done
No need for list of contributors
dialogs frame icon done
Taskbar icon: Did windows, need feedback then we'll do mac. don't know about linux yet.