MDL-41245 fix multiple install, upgrade and uninstallation issues

Includes rework of cache parameter detection on admin/index.php.

Another problem is that uninstall does not leave system in consistent state,
we need to force users to go through upgrade after any type of uninstall.

This fixes also add-on installation redirect and other issues.

lib/adminlib.php

@@ -329,6 +329,9 @@ function uninstall_plugin($type, $name) {
     // Finally purge all caches.
     purge_all_caches();
 
+    // Invalidate the hash used for upgrade detections.
+    set_config('allversionshash', '');
+
     echo $OUTPUT->notification(get_string('success'), 'notifysuccess');
 }