Redeploy plugins on each startup, and provide options for admins to clear the plugin cache through the front end

We have a KB that is referenced a lot in support issues that really could be invalidated by forcing Confluence to rebuild the contents of the plugin-related directories on each startup. We have seen issues persist through restarts that this method will fix, and if a restart could provide the same solution, it would save customers a lot of pain.

Ideally this functionality could also be made available through the front end, so an admin can clear the plugin cache without a restart of the instance.