Implemented first version of a slidable navigation bar.
Merge branch 'master' into feature-slidingnavigation-mab-master

Conflicts:
	Kernel/Output/HTML/Standard/AgentNavigationBar.dtl
	var/httpd/htdocs/skins/Agent/default/css/Core.Header.css
Replaced characters by font awesome icons.
Tidied.
Merge branch 'master' into feature-slidingnavigation-mab-master

Conflicts:
	Kernel/Output/HTML/Standard/AgentNavigationBar.dtl
Fixed: Navigation broken if many modules installed (bug#6802).
Merge branch 'feature-slidingnavigation-mab-master'