We had a number of siteconfig settings leaks between tests, caused by

one test modifying the settings and another utilizing those settings.

This could subtly impact some tests in ways that weren't always clear,

and it could depend on the order in which tests were run or the order in

which events happened. This largely happens because we don't necessarily

fully replace the SiteConfiguration in-between tests, instead often

using a cached copy.
This change updates all individual tests that need to modify siteconfig

to use the siteconfig_settings context manager, which will handle

setting and restoring the settings.
Classes that modify these settings in setUp now ensure they've cleaned

up after themselves in tearDown, preventing further leaks. Some do

this by saving and restoring an individual setting that's modified, and

others save a copy of all settings and restore them, depending on the

needs of the test suite.
Room for improvement going forward would be to add formal support in our

TestCase to let classes define global siteconfig settings and handle

the setting and restoring automatically, to completely remove the need

for custom management of siteconfig, but that's outside the scope of

this change.

All unit tests pass.