Allow for storing and maintaining dietary inputs

[cheddar]

@yrrebnarg states (tidepool-org/data-model#19)

Fat and proteins also affect BGs, as does dietary fiber. While they are not as fast as for carbs, any record keeping utility should include the ability to log these as well. I know from personal experience that a fatty 12oz will have an effect for as long as 12h if I don't cover it with a long and slow extended bolus.

I'm creating this issue to cover the high-level requirement of actually taking in dietary inputs instead of just information from the bolus wizard. As we do that, we should definitely make sure that it is possible to attach protein, fat and whatever other nutrients people decide they care about along with carbs.