progress bar for loading screen

the function “view.setLoading()” should get an optional argument to show the progress of the loading process as in http://getbootstrap.com/components/\#progress
In addition an arbitrary text should be displayed. The function should have the signature

view.setLoading(true/false, progress_in_percent, text=“”)

(from redmine: issue id 2235, created on 2015-06-06 by Christian.Glaser)