Create bgInput field on wizard events to surface BGs entered into wizard

@jebeck @brandonarbiter @skrugman @HowardLook 

This is a proposal for how to resolve the request from Aaron and Brandon for being able to semantically differentiate a finger prick from a value entered into the pump.

The idea is that the wizard event gets a field for the level of blood glucose that was entered into it.  We then need to adjust the front end visualization to be able to visualize wizard-entered blood glucose in some way that differentiates it from `smbg`.

Thoughts?