017-09-11: FG; Changed index.html to make it more general.

	Leave it up to later code (e.g. openstack-dashboard charm) to:
	- subsistute string DASHBOARD_BASEURL (e.g., with https://dashboard.cloud.garr.it)
	- make sure the following paths are properly setup on openstack-dashboard:
	  + /static/dashboard/css/dashboard_css1.css
	  + /static/dashboard/css/dashboard_css2.css
	  + /static/dashboard/js/dashboard_js1.js (referenced in the header section)
	  + /static/dashboard/js/dashboard_js2.js (referenced in the body section)