dynamic dialog size for DialogSelect.xml

This commit adds dynamic sizing to DialogSelect as requested by @Montellese in https://github.com/xbmc/xbmc/pull/5546 and also discussed on forums in http://forum.xbmc.org/showthread.php?tid=206702
It would allow us to get rid of lot of spincontrols in settings area (i hope that most people here agree that using DialogSelect instead of spincontrols is much better to use in most cases)

What I added:
- some slide animations to reposition the dialog when container.numitems is low
- 4 background dialog textures with different sizes, showin up depending on container.numitems.
- visibility condition to container.numitems string to only show up when container.numitems  is high (>8). that label is only needed when the list length requires a scrollbar IMO.

The GitHub Diff Viewer somehow only shows crap  (probably because most part of the xml is indented by one more tab now), the one integrated in SmartGIT works much better in this case if anyone wants to review it properly. ( @ronie @BigNoid ;) ) I think I tested all possible use cases for DialogSelect (list id 3 vs. list id 6, with / without "Get More" button), but another two eyes havin a look into it would be great :)

Small downside: All skinners would have to add something like this to make that dialog look nice with only few listitems. It´s not a lot of work though and nothing will break if those adjustments are not made. It´s still easier to add than a complete new dialog IMO.

SCREENSHOT BEFORE:
![image](https://cloud.githubusercontent.com/assets/110931/4719867/f6b47e2e-592c-11e4-9e79-1eba7e955d1e.png)


SCREENSHOT WITH CHANGES:
![](http://i.imgur.com/tHczB9j.jpg)

Cheers