Several fixes, including improved Date/DateTime support.

- Added `auto` to Date & DateTime
- Added `first` to Date & DateTime
- Made Date/DateTime actually convert to a Date Object.
- Fixed issue in model preparation where we wouldn't send the backend autoid fields, therefore, we didn't know if this was an existing model or a new one.
- Fixed issue in AutoIDField where we'd always return `undefined` for the prepared value; this was silly and wrong.