* Context now allows pinning a datablock, independent of
selection.
* Initial ID browse buttons for most buttons tabs.
* Browsing from world to texture now displays world textures
again, but is a bit of a hack, not sure there is a right
way to do this.
* There's a button to switch between active materials and
textures now, only temporary though.
* There's some code to put context part in own region,
disabled still because it doesn't work that well yet.
* Added panels with dummy preview template.
* Added constraints panel for bones next to objects, though it
doesn't work that well yet, the operators and code need to be
changed so they don't assume it is one or the other in/out
of posemode.
* Added some graying out in the scene and world buttons.
