working indicator

Where is the indicator used?:
- on batch update.
- on every attempt to fetch a collection. To see it you would need to set bootstrapped data to false in /public/app/browseWorks.js : 146;
- while saving an edited work
It should be possible to construct the whole HTML in one call:

    $(this.el).prepend('<div class="overlay"><div class="loading"></div></div>');