Imagefactory for XBMC

What this pr does:

1) implements a factory for image libraries similar to the ones we have for codecs and filesystems
2) modifies imagelib and JpegIO to use our vfs instead their own routines

I didn't touched code for android/rpi but I guess their code could be easily implemented afterwards. 
It needs some love on Linux/OSX and ofc testing on all platforms.

Don't look too closely on the imagelib changes as I plan to replace it with freeimage (not started yet).
This is ofc Frodo +1