Cache-friendly new version :)

Okay, this version will use "legacy" (cached) requests until this is implemented:

`PROXY_THRESHOLD_URL = 'http://plexapp.com/proxy_status.php?agent=com.plexapp.agents.lastfm' # This should return desired percentage of "new style" requests.`

(this is a pie-in-the-sky suggestion, ofc, I gave this request a cache time of five minutes with the idea being that something could monitor the proxy server and feed back a desired percentage of new requests in semi-real-time...)