artwork: add "Add art" button to video artwork selection dialog
added an imagefactory to XBMC. The only libs currently are libjpeg-turbo and cximage.
Merge pull request #2040 from wsoltys/imagefactory

Imagefactory for XBMC
Merge pull request #2163 from Montellese/artwork_add

add "Add art" button to video artwork selection dialog