Fixed vertical menu label alignment.
Don't use the new synchronous mechanism for loading external optional scripts specified by plugins. It breaks any secondary references the script may use internally (ACE for example). The old load logic has been reintroduced as 'add_script' in utils.js and the logic in core has been changed to use this instad of the new version of load_script.
Reintroduced the behaviour to explicitly stop playback before loading a new sequence.