A testcase mixin for resetting the state of avatar services.
The avatar service registry class will change the state of the
SiteConfiguration.settingsobject, which will not be automatically undone when the test-case finishes. Instead, we cache the site configuration settings prior to running any test cases and reset the site configuration settings to these cached settings after each test.
This mixin should be used in any test case class that deals with avatar services.
Cache the SiteConfiguration settings object.
Restore the SiteConfiguration settings object.