Download progress is not displayed

[mcepl]

Together with #4 it is really difficult to know how far we are in the downloading episodes’ media files, and especially when it is the time when all media files have been downloaded, so that the phone can be switch to the offline state.

[colinfrei]

I can't actually display the progress until angular/angular.js#3606 (or something that does the same) is merged, I did add an indicator that something is happening in 463fd6d though.