Merge branch 'master' into UI-graphical-redesign

Conflicts:
source/blender/blenkernel/BKE_blender.h
source/blender/blenloader/intern/versioning_270.c
source/blender/editors/interface/interface.c
source/blender/editors/interface/interface_handlers.c
source/blender/editors/interface/interface_intern.h
source/blender/editors/interface/resources.c

Merge branch 'master' into UI-graphical-redesign

Conflicts:
source/blender/blenkernel/BKE_blender.h
source/blender/blenloader/intern/versioning_270.c
source/blender/editors/interface/resources.c
source/blender/makesdna/DNA_userdef_types.h

Merge branch 'master' into UI-graphical-redesign

Conflicts:
source/blender/blenkernel/BKE_blender.h
source/blender/editors/interface/resources.c

Merge branch 'master' into UI-graphical-redesign

Minor theme change

Add an "Interface Style" theme option for flat vs. classic drawing

Adds an "Interface Style" menu containing the items "Flat" (default) and
"Classic". The classic option basically brings back widget outlines,
emboss, shading and old checkbox design.

Open design question:
Currently widget outlines, emboss and shading is hardcoded disabled for
the "Flat" option. Meaning that tweaks to their theme options don't have
any effect. I think it should be fine to just disable the theme buttons
for this, but I'm all ears for better approaches.

Requested by @campbellbarton and @ton

Draw widget boxes antialiased

Better drawing for checkboxes (perfectly round + anti-aliasing)

Merge branch 'master' into UI-graphical-redesign

Add widget rollover feedback by implementing a Sub-Button pipeline

As pretty much agreed on in T38070, this implements widget-rollover for
better visual feedback.
The added Sub-Button pipeline should provide us a solid base for future
ideas like using Sub-Buttons to trigger operators (thinking of 'X'-icons
within tabs or menus e.g.), open popups/menus, provide better cursor
feedback, etc. They are basically independent buttons within buttons.

https://developer.blender.org/F187781

Merge branch 'master' into UI-graphical-redesign

Fix Clip Editor not using correct scrollbars in Graph/Dopesheet view

Merge branch 'master' into UI-graphical-redesign

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

Use left aligned text for icon buttons

Merge branch 'master' into UI-graphical-redesign

Use thinner scrollbars for UILists as well

Todo: With the current default theme scrollbars are hard to see, we
could do better but that's for later.

Adjust some theme colors

And the usual minor cleanup

Cleanup: Use existing methods to init new/changed theme options

Think this is the way we should actually do this.

Fix panels being highlighted while dragging another panel over them