UI: Vertical Properties Editor Tabs
Moves the Properties editor context switching to a vertical tabs region.
Design Task: T54951
The tabs are regular widgets, unlike the 'old' toolshelf tabs. This means they give mouse hover feedback, have tooltips, support the right-click menu, etc. Also, when vertical screen space gets tight, the tabs can be scrolled, they don't shrink like the toolshelf ones.
The tab region is slightly larger than the header. The tabs are scaled up accordingly. This makes them nicely readable.
The header is quite empty now. As shown in T54951, we wanted to have a search button there. This should be added next.
- Added a new region type, RGN_TYPE_NAVIGATION. Although this could be avoided, I think it might be useful for T54115. Also, this allows theming the background.
- Having the tabs in a separate region allows scrolling of the tab-bar, unlike the toolshelf tabs.
- Added a new region flag RGN_FLAG_PREFSIZE_OR_HIDDEN, to ensure the tab region is either hidden or has a fixed size.
- Added some additional flags to support fine-tuning the layout in panel and layout code.
- Bumps subversion.
- Updates the default theme file.
- There are a few minor TODOs marked in code that I plan to address before committing.