Add device management tab

- Tidy up sensors model.
- Fix delete and user editable keys.
- Use inserts in devices PUT since it works like update.
- Add new sensors and new devices and edit them.
- Make alert a component.
- Show alerts on successful events.
- Add number of sensors per device.
Fix alert component and make fetching fns variadic.
Fix sensor schema and reorder fetching fns.
Merge pull request #146 from MastodonC/feature/new-device-sensor-ui

Add device management tab