Refine unit reduction algorithm

[isaaclafrance]

Two approaches with different performance outcomes will be employed to reduced a provided unit definition into a smaller equivalent definition within a specified unit system. The first approach involves transforming the provided unit definition to a more condensed fundamental units dimension with identical units cancelled where appropriate. If necessary, this more condensed dimension will be matched against similar existing precreated units in the units repository that are smaller and having the specified unit system. In the second approach, the provided dimension will also be condensed and there will also be a matching stage, but matching will be more complicated than just a simple straightforward comparison of the whole dimension; instead the dimension will be partitioned into different combinations and permutations that will be matched and the partition match result chucks will subsequently be recombined. Consequently, this second approach will be a bit more involved and perhaps less performant, but will hopefully allow for a more complete reduction result. However, in most situation, the first approach should be satisfactory.