Fix a flaky test condition that only occurs in
multiprocessing mode. Make the page definition more
specific; the previous implementation would not fully
render all objects in time.
Avoid race condition related to events order (in faster,
multiprocess testing, the order is not exactly the same since
some events arrive at once).
There's a lot of useful things in PR #8271 that provide a framework
for the comprehensive theming system. If we need to remove the edx.org
theme from the codebase, we can leave most of PR #8271 in, to make it
easier to build on top of and get this feature back in.
