Loadnsave (fixes #23)

This branch includes [localforage (a neat wrapper for browser storage)](https://hacks.mozilla.org/2014/02/localforage-offline-storage-improved/) and uses it to store and load application state.

State is for now:
* the list of input files with their content
* the current results
* the state of the checkboxes
* the index of the currently active file in codemirror

I have added two simple buttons, Load and Save to the HTML bits, while loading is quite obvious, from a usability perspective, saving comes with zero visual feedback. 
Some sort of error/info thing is already in place with `$scope.error` but it needs better handling, that I would like to defer to another issue (filing right now..)

Please test and play around before review/merge. I'd like to get some real usage feedback on this one :)