Changes to display basals from new data model

@jebeck @kentquirk 

These are the changes required for tideline to be able to render basals from the new data model.
Do you mind if I move this out into a function in `js/data/util/datetime.js`. Trying to factor all the datetime-related functions into one place for eventual replacement by sundial. Also, moment is not a dependency for tideline (it's a devDependency right now just for some test-related stuff).