Changes for SDK 2

Not sure if you've had time to work on the changes for SDK 2, and I was interested in an updated version, so I got to work.  The changes aren't too bad, and all of these seem to work.

Note that the web app also requires a few changes due to some of the pebble format changes.  I've made the necessary changes in my gh-pages branch and everything seems to work: http://truejournals.github.io/pTOTP/

If you'd like, I can send another pull request for the gh-pages branch either now, or some time later.