Previously, ExpansionPanel would do weird things if interacted with
when it was already animating. This is fixed and there's now a test.
Also:
* Minor fixes to make the gallery work in RTL, not that there's
any way to see that without hard-coding the framework to RTL.
But at least I'll be less annoyed when doing that.
* Some trivial code and documentation cleanup.
c97fc2063f