Delta BG Support

Scott's PR #249 was the starting point, but needed a few changes to work with dev.  Added retro support and fixed a few things.  Delta color follows BG and trend.  Kate helped with MMOL support and layout.  

I added delta to the alarm button, which works for alerts > 40 and < 400, but not HIGH, LOW or Dex error conditions.  Delta should only be in alarm button conditionally.

![screen shot 2014-11-16 at 8 54 12 am](https://cloud.githubusercontent.com/assets/6069420/5062311/cc03a2c4-6d70-11e4-9387-5613a2748bea.png)

![screen shot 2014-11-16 at 8 54 30 am](https://cloud.githubusercontent.com/assets/6069420/5062312/cc06d85e-6d70-11e4-87f2-d60593cb2e59.png)