Blender Git Loki

- expanded internal windowmanager that it allows button panels in any
window (type)
- each SpaceData struct (not the window!) can get 'block handlers'
assigned, basically event codes that invoke drawing button panels.
- this is saved in files, and Panels behave in any window like it does now
in buttonswindow
- it also means that a 'space window' should leave with a matrix set for
buttons level
- try it in view3d header menu, 'view'->'backdrop'. this opens the old
viewbuttons
- it all works non blocking! instant updates of viewbuttons visible in
3d window now.

Not done yet:
- checking and fixing frontbuffer drawing (select a wireframe draws over)
- temporally vertices cannot be selected, is my next project
- closing or hiding Panels...
- styling stuff... i committed for others to review as well.

Have fun. this is certainly a huge improvement over the old viewbuttons!