pvr.DVBViewer: various improvements, bugfixes + basic timeshift support

Hi,

this new version includes various improvements (including basic timeshift support), a massive code clean up and reorganization (the two messy commits) as well as a few bug fixes. A600, the old maintainer, hasn't responded to my pull request for two months now, so I hope to take over main development for his pvr.

It's been tested on win32, x86_64, x86 and rpi (raspbmc).

Regarding https://github.com/opdenkamp/xbmc-pvr-addons/pull/182: Portisch has developed a few improvements in parallel to me. He isn't that familiar with git and linux but we are currently in contact to merge his changes into my repo so we get the best of both. So please decline *his* (edit: not mine) pull request for now.

Regarding frodo: The same improvements for frodo can be found in my frodo-branch. I'm not that familiar with the XBMC development process but if there will be another frodo bugfix release, you can either pull directly or I can open another pull request for you.