UI: Only set custom checkbox and radio icons on abyss, skin icon config now overrides iconset icon config

(integrated from komodo (trunk) change 81555 by nathanr)

git-svn-id: http://svn.openkomodo.com/repos/openkomodo/trunk@13506 b87d16e7-d29f-4ee1-b5ec-817d645d335f
fix: UI: Fix menuitem icons not showing on Mac due to css being overwritten

(integrated from komodo (trunk) change 81556 by nathanr)

git-svn-id: http://svn.openkomodo.com/repos/openkomodo/trunk@13507 b87d16e7-d29f-4ee1-b5ec-817d645d335f