Add cover art column to librarymodel - it will show the covers
Add CoverArtDelegate class - it will be responsible for drawing the cover arts in the tableview
CoverArtCache::requestPixmap(..) - returning QPixmap
- it will be useful for CoverArtDelegate
CoverCache - new argument to check if it must emit "pixmapFound" signals
- CoverDelegate will not use these signals, so it is important not swell up the qt queue.
CoverDelegate - requesting pixmap from CoverCache
covercache - wrong order of member initialization
Merge branch 'coverArtSupport_2' of https://github.com/cardinot/mixxx into coverArtSupport_3
CoverDelegate - small fixes + highlight selected rows
Changes return of CoverCache::requestPixmap(..) to null pixmap + do not draw default covers on tableview
CoverDelegate - setting render hint to use SmoothPixmapTransform
CoverDelegate - avoids drawing default_cover
CoverDelegate - avoids calling "requestPixmap(..)" when the cover is default
tablemodel - using cover_art field as readOnly (disable text edition)
Merge branch 'coverArtSupport_2' of https://github.com/cardinot/mixxx into coverArtSupport_3
Add cover_art column to playlistmodel
Cosmetic fixes to playlistmodel - using sql words in capital letters + using constant strings
librarytablemodel - fixing columns of TEMPORARY VIEW table
Add cover_art column to cratetablemodel
Cosmetic fixes for cratetablemodel - using sql words in capital letters + using constant strings of librarytable
Merge branch 'coverArtSupport_2' of https://github.com/cardinot/mixxx into coverArtSupport_3

Conflicts:
	src/library/coverartcache.cpp