Added new template for choosing to use any type of ID-block. The first combo box allows you to choose the type of ID-block that gets used, and the second box allows you to choose the ID-block of the type specified by the first one.
This is currently used for setting the ID-block used for Keying Sets, but the main user for this was intended to be the Drivers UI. However, I still need to clear up a few button-event issues there before I can port this over.
Additional Bugfixes:
* Adding new Keying Set path was setting the active path wrong, meaning that you had to click on the list to get some response after adding
* Bone Groups list was being drawn too long by default (when empty)
