adds regex to grunt and fixes CSS image urls

Conflicts:
	geonode/static/gruntfile.js
removes images from lib/css
Merge pull request #1028 from cspanring/grunt

adds regex to grunt and fixes CSS image urls to use one consistent path (lib/img)
Merge remote-tracking branch 'geonode/master'

Conflicts:
	geonode/static/gruntfile.js
	geonode/static/lib/img/spinner.gif
cleanup: removes obsolete bower-installer config