Merge pull request #28 from cboxdoerfer/master

gtkui: make appearence (fonts/colors) more configurable
Callback mutextes, encapsulate cache cleaner
cocoa: design mode WIP
Tracing off
Handle no cache expiry time better
Merge pull request #29 from Lithopsian/artwork

Possible freezing fix
osx: few optimizations
Two mutexes to minimise blocking
Path length safety, terminate cleanly when cache period = 0
Zero length artwork not accepted, more mutex locking stuff
Handle mutex errors
Merge pull request #30 from Lithopsian/artwork

Artwork fixes
cocoa: slight seekbar optimization
Fix cache reset and expired pixbuf cache (see issue #1179)
Merge pull request #31 from Lithopsian/artwork

Fix cache reset and expired pixbuf cache (see issue #1179)
Remove expired cache pixbuf, don't just ignore it
Merge pull request #32 from Lithopsian/artwork

Remove expired cache pixbuf, don't just ignore it
cocoa: new seekbar drawing
cocoa: hide test window
cocoa: more seekbar improvements; added window menu; added restoring mainwin after close