Fix bug with Plex connector not detecting playback

I noticed that playing music from my Plex server, though the icon in my browser showed
that the site (my PMS instance) is supported for scrobbling, no playback notifications
ever appeared. I did a little digging and discovered that .live() is deprecated in
latest jQuery; we should use .on() instead (or .delegate(), if absolutely necessary).

In fact, testing $('div#plex.application').live(); in the JS console with my Plex server
open and the scrobbler icon active in my location bar returned a TypeError: undefined is
not a function. However, $('dig#plex.application').on(); works fine.