Add progress bar to photo upload progress notification (#379)

The progress bar shows up only on phones that support it (tested on
Safari from iOS 6 and Chrome for Android). As a fallback, the message is
also alternated every 10 seconds as #379 suggests.

Also:

* Created a generic ProgressBar which can be reused in other places.
* Allow views to define class of their parent $el element (reduces
  divitis, helps with styling).

Change-Id: Id124b7c99a4d1dce3a3d28e1b5d88d7dc8d649bc