Optimize Combination Generation

[marciosarto]

Currently the whole load combination is performed at each TimberFramePoint generated from the Karamba import. This is making the conversion really slow.

Solution:

Create a CombinationStorage class that retrieves the load cases and returns a list with the final multiplication factor for each load case, as well the combination string.

With the combination stored in this object, we just need to calculate them once and basically directly generate the combinations in the TimberFramePoints from the combinations list.