[Feature Request] Autohandle units for CapacityToActivity

[samgdotson]

Currently, users must manually supply a value for the capacity_to_acitivity of each technology. This should be handled automatically with a tool such as Pint.

Technologies and commodities each have units specified as strings. Ideally units would be Pint objects that can be manipulated easily.

**The capacity to activity value is understood as "the amount of a commodity that can be produced by a certain capacity in 1 year." It is not related to capacity factor, it just tells Temoa how the units shakeout."

This issue can be closed when

• there is a file in utils/ called units.py
• Pint (or similar tool) has been added to the requirements.txt file.
• the units.py file has functions to convert units and return a capacity to activity.
• there are corresponding tests for units.py in the tests/ folder.

One of the following

• the function create_capacity_to_activity() in db_creator.py should be updated to automate the unit conversion
  OR
• the Technology class should have a function that automatically calculates the C2A.