Update to support SDK 2.0

Hi there,

I'm sending you this pull request because I forked your tea_timer app and updated it for SDK 2.0. I'm sending this pull request in case you wanted to merge it into your own codebase.

Note that I've also made a few other changes:
* Larger font
* Swapped up and down buttons (up->reduce time, down->increase time; this matches the next/prev behaviour in builtin music app)
* Add ability to stop & start timer
* Snap timer changes to nearest 30 seconds
* Changed default time to three minutes

I've included these in the pull request, but if you want any of them removed, let me know and I'll revert them and resubmit the pull request.

Alternatively, feel free to ignore me and I won't bother you again. :)

Thanks in advance,
Bennett.