Add Backbone + structure

Create basic app structure using Backbone & Marionette.
Don't include utils.js because I don't think it's used
Backbone-ify old SampleEditor class code
Make the add button semi-work

Paste a URL, click the '+' button, and a new sample progress bar
appears on the page (woo!).

TODO: initialise drag handles on add of a new sample progress bar
Merge branch 'add-sample-to-collection'