DVBViewer: use RS XML API, partly rewritten, more bugfixes

Update for dvbviewer pvr. Part of these changes are features from Portisch work. But there's still stuff left.
I want these merged as the current nightly code doesn't work for a lot of people due to the two crash/mem corruption fixes.

Changes:
* Require DVB Viewer Recording Service 1.25.0 or later
* In general use RS XML API instead of HTML/channeldat parsing
* Rewrote channel parsing. Use favourites if you want fast startups.
* Rewrote recording parsing, generate unique recording IDs
* Show available diskspace
* RTSP support (Note: RTSP is only available if timeshift is disabled)
* Removed signal status information. Not available anymore
* Fix channel logos not being displayed for some channels
* After changing certain settings live TV wasn't work anymore and XBMC restart was required
* fix possible crash/memory corruption (2x)