add rate to basals of deliveryType 'suspend'

Yesterday I missed the fact that @cheddar had omitted the `rate` from basals with a `deliveryType` of `suspend`. I believe that this field should be included, even though it is always 0.0 for this `deliveryType`. The fact that the visualization code needs a rate to calculate the height of the path is irrelevant when discussing the storage data model, so I won't make *that* argument here. The argument I will make is that events of type `basal` represent the delivery of insulin in some form (for `deliveryType: injected` this is a `value` field instead of `rate`), and it feels sloppy to me to force users of the data to infer the actual amount of insulin delivery from the `deliveryType` in some cases.

Whoever wants to weigh in on this, please do: @kentquirk @jh-bate @ianjorgensen @brandonarbiter @HowardLook