Blender Git Loki

A first Menu/Popup redesign

Based on this mockup by @venomgfx: http://wiki.blender.org/index.php/
User:Venomgfx/User_Interface#Menu_Item_.26_Menu_Back

Main changes:
* Draw background for menu title in a different color (currently
hardcoded darker) instead of using a separation line
* Align submenu triangle icons vertically and add some extra space for
them so that they are not squashed in to the line (means shortcut text
is now always vertically aligned as well)
* More modern submenu triangle icon drawing
* Draw separation lines a bit more visible
* Don't add extra icon padding if the menu doesn't contain any icons
(text in menus often used to have some padding on the left so that the
text is nicely aligned even when some entries had icons in front of it.
This is all fine but wasn't needed/looked weird if there isn't any menu
entry with an icon at all - e.g. 3D View "Select" menu, most of the RMB-
menus)
* Cleanup

Screenshots:
* https://developer.blender.org/F185706
* https://developer.blender.org/F185707
* https://developer.blender.org/F185708