Fixed the cached extensions issue.Previously newly installed/removed extensions required re-starting Django. This fix, forces flushing the extension cache everytime the extension list view is called upon & any updates are reflected.

Installed and removed ReviewBot extension on the original codebase. On both instances, the plugin didn't show up on a page refresh at /admin/extensions until Django was restarted. Forcing the cache to be flushed, makes the removal or addition of extension show up on a page refresh now.

Units tests are okay as well.