Tidy constraints module

[tsmbland]

I imagine this will have horrible merge conflicts once #550 is merged, so I'll write out the main ideas in this PR but it may be better to start again fresh. This PR also probably messes up the trade feature which I don't want to do, so I'll need to be more careful with that if/when I try again. It will help when #572 is done.

Main changes:

• Pass technology parameters only from the current year to the constraints. I'm not actually sure whether this should be from the current year or the investment year, but that would be easy to change. The point is that constraints are based on a single parameter set
• Don't pass the whole market object, extract capacity data from the market object and pass that directly (since the constraints currently don't need any other data from the market object). Capacity data has two years: current year and investment year/
• Don't pass assets to the constraints - not required
• Check input dimensions before passing to constraints
• Update tests accordingly

The main idea is that constraints only get passed data that they need, which makes to code more readable and gives less room for errors

[tsmbland]

Closing as this will likely never be merged, but I've listed out the main intentions above in case I want to return to this later