lib/plugin.php now has a parent onAutoload function that finds most common
files that are used in plugins (actions, dataobjects, forms, libs etc.) if
they are put in the standardised directories ('actions', 'classes', 'forms',
'lib' and perhaps some others in the future).
'admin' is a pretty common username that people try when installing;
it was blacklisted because all of our admin panels were at /admin/*,
which would conflict with the admin user's namespace.
Changed the location of all admin panels to /panel/*, blacklisted the
nickname 'panel', and allowed 'admin'. Tested with a fresh install;
seems to work great.
