Pylitterbot

Change cycle_capacity to calculation to avoid reporting >100% waste_drawer_level
Add class method to LitterBoxStatus to retrieve drawer full statuses and include a minimum_cycles_left property
Remove const.py and move items to robot.py since it really is only related to the Litter-Robot

Add model to robot and slightly adjust how sleep_mode_start_time and sleep_mode_end_time are calculated
Adjusted set_sleep_mode to allow not passing in a time when turning on, which will default to the previous sleep_mode_start_time or the current time if that is empty
Create utils file to separate some logic
Additional code cleanup and organizing

Breaking Changes
Robot.UnitStatus enum was revamped so as to provide more detail:
- all Enum members have changed:
- `UnitStatus.BR` is now `UnitStatus.BONNET_REMOVED`
- `UnitStatus.RDY` is now `UnitStatus.READY`
- etc
- to get the "code", you now use the `.value` property (previously was retrieved by using `.name`)
- to get the text, you use the `.label` property (previously was retrieved by using `.value`)
- a few text values also changed, such as that for DF1/DF2

Other Changes
Now uses the method from the newer app to set sleep mode to avoid start time "drift". If you use the older "Litter-Robot" app instead of the "AutoPets Connect" app, you may see discrepancies in the sleep mode start time if you continue to set the sleep mode time from the "Litter-Robot" app.
`sleep_mode_start_time` and `sleep_mode_end_time` may now both have values even if `sleep_mode_active` is false

Adjust UnitStatus text

Handle ConnectTimeout exception

Fix default cycle count/capacity