* 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.
Separated out the code for defining the layout for the constraint targets since its practically the same (with a few minor variations) for all of the other constraints.
* Added Constraints template and Add Constraint operator.
* Added toggle=True/False parameter to uiItemR, to get a
toggle button (actual button) rather than an "option"
button (checkbox)
* Added OPTION/OPTIONN button type, to distinguish with
TOG/TOGN.
RNA:
* Make all modifier pointers editable, including correct updates.
* Added notifiers and updates to constraints.
* Fix a stack corruption, pointed out by Andrea, and potentially
causing crashes.
