Add option for a suspended basal

@jebeck @kentquirk 

This is an extension to the data model to allow a pump to create a meaningful stream of basals in the case of a suspend (i.e. it is possible for an integration to tell us about the actual basals delivered with just basal events).  The idea is that when a suspend actually happens, the pump will now have something that it can use to provide us with meaningful basal information.

Please look this over and comment as soon as you see this, 'cause I am already working on it.
What kinds of circumstances do you imagine where there's no suppressed? When a suspend occurs before switching devices or...?