artwork: configurable no-artwork image, style pref dialog, make no-artwork respond to pref changes
coverart: fixed pixbuf scaling and position within the widget
coverart: data types for Cairo calls
coverart: clean up old default pixbufs
Merge pull request #57 from Lithopsian/search

Configurable image for missing artwork, pref dialog, fix for Widget scaling (issues #655, #724, and #1222)