Add filters AFTER plugins have loaded

The shunts that this plugin uses to disable tracking of admins are added when the plugin is loaded. yourls_is_valid_user() is used to determine if the shunts should be active/added or not.

hooks can be called by yourls_is_valid_user(), but because the function is called during plugin initialization it is possible that other plugins have not initialized (and have not added actions/filters related to authorization).

The solution is to wait with added the shunts until all other plugins have loaded.