Add embedded player on mainpage, using JPlayer

Advanced embedded player on the bottom mainpage using iframes. Better user experience and avoid popup.
See screenshot bellow.
![ampache_embedded_player](https://f.cloud.github.com/assets/2251352/1394417/25ca0f20-3c29-11e3-9a51-5c0150498cec.png)

Iframes remains optional, you have to enable it (after database update) on Preferences => Interface and set 'Iframes' to Enabled. Then refresh the page and select the new player 'Iframed Player'. Player will be displayed at first listening.

It's something asked several times by people that I know and even here (#61 and ticket 22 on previous issue system), hope it match most needs.
Its using JPlayer, that means the player is also fully HTML5 (tested on Chrome/Firefox, Windows/Linux ; can fallback to flash) and by the way partially answer current user requests: #63 #59 #

It's my first contribution on Ampache, I could have miss some important architecture points but should be good enough. Let me know if changes are required for merge.