Commits necessary to upgrade manifest version

I found these two commits necessary to get the extension to work correctly in recent Chrome versions where the new security restrictions are enforced.

I'm currently playing around with synchronizing config between browsers using Chrome Sync and later maybe some other synchronization method.  The secret seeds won't be synchronized but will stay in local storage.

That work has required me to change all of the synchronous calls to localStorage to an asynchronous API (call storage api and pass a callback).  I wrapped localStorage with an API that acts like an asynchronous API so that using localStorage is still the default option.  The changes are rather intrusive but necessary in order to make use of Chrome's storage API.  Are you interested in seeing and possibly consuming that work?  I'm still testing and probably won't publish until it is working well.