Description

This is a small change to make the MaxCapacityAddition, MaxCapacityGrowth and TotalCapacityLimit parameters optional.

I've found that many users just set these to very high values so that the constraint effectively doesn't apply, but this is annoying and messy.

It's already possible to exclude this constraint by modifying constraints in settings.toml, but this is a bit fiddly and in general I don't think users should be modifying constraints (I encourage users to leave this out of their settings files so all the constraints are used by default).

I think the change here to make these parameters optional is more user friendly, as all users need to do now is delete the relevant columns if they don't want to use the constraint for that sector.

Close #667

Type of change

• New feature (non-breaking change which adds functionality)
• Optimization (non-breaking, back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (whatever its nature)

Key checklist

• All tests pass: $ python -m pytest
• The documentation builds and looks OK: $ python -m sphinx -b html docs docs/build

Further checks

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works