Universe: custom update handler.

This depends on #127 , changing and saving a playlist now properly updates
between different browser windows. I know it looks dirty.

KB doesn't like when the default handler for the 'update' event does

    item.set(data_from_server)

and it overwrites item.collection with another one, so instead of that
we update the original collection with the new data.

Signed-off-by: Adrian Pardini <github@tangopardo.com.ar>