* Fix context.cloth, was not being set correct.
* Fix errors with context pinning, scripts should
not assume context.object to be there.
* Always show preview even if e.g. the material is not
set, to keep ID buttons from jumping while you're
using them.
* Added more material buttons by William. Thanks.
I made some minor adjustments and added Specular Shader Model RNA.
* Code cleanup and some consistency tweaks of button files.
Notes: Preview render now only shows up when there is an active world, material, texture or lamp.
* Made sure initial panels with ID Datablocks are shown, even when no block is active.
* 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.
