ADD: Caching of XML responses and Server Lists (1 hour)

Improves subsequent load times of all lists and key frequently used
methods.
Requires/Depends on "Common Plugin Cache" available via the XBMC
repository.
FIX: "Unable to load script" when entering context menus

When installing the "frodo" version of the plugin the plugin folder is
"plugin.video.plexbmc-frodo" and not "plugin.video.plexbmc".
Various list based context menu items which self called the script
failed (e.g PlexBMC Settings)
FIX: Transcoding audio streams not correct as per Settings

When testing with PMS it would always use the first value specified and
ignore the other values. (AC3 would still result in mp3)
If the user explicitly specifies AC3 or DTS then they would presumable
want 5.1 audio?

Other notes: Audio transcoding could be extended further by allowing the
user to specify the Audio Bitrate in settings and it be set using
<codec>{bitrate:xxxx&channels:x}

Would help keep control of those pesky high bitrate audio tracks :)