[Bf-interface] GUI redesign - Call for Participation ;)

[Julian Eisel]

Hey all!

I guess most of you already noted that I was working on a graphical
redesign branch for a couple of days now. So far this was mostly
fooling around since we discussed a lot about many things but didn't
make many desicions. So currently I've implemented a mixture of
different proposals/styles.

Main changes so far:
* "Interface Style" option to toggle between old "Classic" style and
new "Flat" style
* Implemented a Sub-Button pipline for widget rollover feedback (Task:
https://developer.blender.org/T38070) but can be used for much more
* New panel design (Task: https://developer.blender.org/T41261)
* Improved Menu/Popup design
* More flat widget drawing (disabled outlines, emboss and shading -
Task: https://developer.blender.org/T38037)
* Increased default DPI to 78 (was 72), decreased font sizes
* New Area/Region edge design, also added a theme color option for it
(mainly for testing)
* Thinner scrollbars
* Theme option for widget corner roundness (mainly for testing, don't
think we should have that in master TBH - based on an old patch from
Pablo)
* New checkbox button design

Some screenshots of the current state of the branch:
* Full default screen: https://developer.blender.org/F188930
* Sub-buttons widget rollover (.gif) https://developer.blender.org/F187781
* New menu design: https://developer.blender.org/F185707
* "Interface Style" menu: https://developer.blender.org/F188942
* "Classic" style: https://developer.blender.org/F188937

Up till now, I've mostly worked on my own, asking Pawel for new ideas,
feedback and mockups now and then, but think at this point it would be
good to join forces on this (at least the UI team).
First some general feedback on status quo would be good, but then we
should start looking into some details, make desicions and also work
on the new default theme(s).
The exact branch name is UI-graphical-redesign btw, but the
UI-experiments branch is in sync with it.

So! I see this as a good chance to prove (find?) the power of the UI
team and as a good warm up project for more, hope we can get something
done :)

Cheers,
- Julian -