[pvr] Rewrite of PVR window integration

As pointed out on IRC i'm working on a rewrite of the current PVR window integration. I've refactored all "sub windows" 
(channels, guide, recordings, timers, seach) out of CGUIWindowPVR to be normal windows which inherit from a CGUIWindowPVRBase class 
(same it is done on other parts of XBMC). Each window has its own new window id depends on the type tv or radio (_WINDOW_TV_CHANNELS, WINDOW_RADIO_CHANNELS, WINDOW_TV_GUIDE_ etc.) 
and is mapped to an action command (TVChannels, RadioChannels, TVGuide etc.) within the CButtonTranslator. You could activate such a window by calling 
`ActivateWindow(TVGuide)` or `ActivateWindow(RadioGuide)`. 
I also changed the implementation of views to be dynamic such as the video views are, except the guide views which need static ID refs (10 = epggrid, 11 = now, 12 = next, 13 = channel epg). 
But the skinners will have control over which views are used by adding them to the `<views>` node. So now it's possible to add different views for channel list, 
recordings etc. or for example only provide the guide grid view for the guide window by adding the ID 11 to `<views>` only.

There are several other changes, so here is complete overview:

* new windows ID's: _WINDOW_TV_CHANNELS, WINDOW_TV_GUIDE, WINDOW_TV_RECORDINGS, WINDOW_TV_TIMERS, WINDOW_TV_SEARCH, WINDOW_RADIO_CHANNELS, WINDOW_RADIO_GUIDE, WINDOW_RADIO_RECORDINGS, WINDOW_RADIO_TIMERS, WINDOW_RADIO_SEARCH_
* new window action mappings: _TVChannels, TVGuide, TVRecordings, TVTimers, TVSearch, RadioChannels, RadioGuide, RadioRecordings, RadioTimers, RadioSearch_
* use of ```ActivateWindow(TVGuide)``` instead of ```ActivateWindowAndFocus(MyPVR, 31,0, 10,0)```
* get rid of static button references for activating a pvr window (heavily used on the sideblade menu), instead ```<onclick>ActivateWindow(TVGuide)</onclick>``` is used.
* new group selection dialog (Button control ID: 28)
* use of the "View As" button (ID: 2) to switch between existing views.
* new gui info properties _PVR.HasTVChannels_ and _PVR.HasRadioChannels_ to determine if we have tv and/or radio channels and hide the tv/radio item in home menu.
* new window property _IsRadio_

It would be nice to get some feedback especially from @jmarshallnz for the gui part, @opdenkamp and @Jalle19 for the PVR related parts and @ronie for the changes I made to confluence.
minor nitpicking, but could you add the string as a comment behind these and the one below. code doesn't tell what we're telling the user otherwise