Ability to change the properties of multiple items at once in the properties pane

[vlidholt]

Ability to change the properties of multiple items at once in the properties pane, assuming the selected items share the same properties.

[LearnCocos2D]

Feel free to assign this to me when the time comes. I've worked on several tools with that exact problem, and I have a "user" right here who I can ask how it worked in tool X or Y or what he'd expect to happen.