support for global proxy conf
add documentation for proxy usage
having some fun with background images and css3 cover property
Merge branch 'master' into tk-admin-interface

Conflicts:
	Gruntfile.js
	public/css/custom.css
	public/js/modules/git/backend.js
	public/js/modules/github/backend.js
	public/js/modules/jenkins/backend.js
	public/js/modules/trello/backend.js
	public/js/modules/twitter/backend.js
	src/office-module.js
	src/server.js
use -proxy option from grunt to disable proxy