Glowmarktha

- Bit more typing
- Add separate object and method for checking auth

- Adds handling of consumption periods other than P1Y
- Fixes standing charge constant used in `Utility.get_tariff`

- Adds time zone information to datetimes
- Fixes the `Utility.get_tarriff()` method

Ensure that the end time of `Consumption` is actually the end, not you know, the start

**Full Changelog**: https://github.com/TomBrien/glowmarkt-ha/compare/0.0.4...0.0.5

Fixes to constants

Add consumption function