Opinion: all of the save<Activity> methods should use the same properties as Apple

[CodySummers]

For example from what I can tell most methods use startDate and endDate when saving and retrieving properties. However the odd one in this wrapper uses date e.g. saveWater and saveBmi (which should also change to saveBodyMassIndex), uses date while saveWater does say in this wrappers docs to use date, saveBmi doesn't.