New optimise load profile functionality

[wouterpeere]

Currently, the optimise_load_profile function assumes that all years are equal. By doing this, you optimise from a power perspective: i.e. the highest amount of power you can put onto the borefield.

However, when looking at this problem from an energy perspective, there is still a lot of potential, in the non-limiting years.
This issue is related to the development of a new method that optimises the load profile from an energy perspective instead of a power-perspective.