RapidXML Integration rather than using TinyXML

This Boosts up the xml parsing by a ratio of aboux X100 :)
Setting RapidXML as default parser

This could be nicely also replaced by a compilation define
Fix for commit 3372e11aaafc78145deae60891208a61a16ee76d

Oops, forgot to add something after code cleaning and before the commit
:)
Plex Global Cacher

This will add a global caching mechanism in order to  startup cache all
the thumbnails locally on a fresh startup. it will create a plex.cached
in userdata directory when it has been done at least once in order not
to reprocess at every start