Adding the ability to handle "complex" point mutations

[emarinier]

Adds the ability for starAMR to handle "complex" point mutations. That is, mutations where several individual point mutations are simultaneously required to confer a phenotype.

The solution has been created for Enterococcus faecium, but the framework should allow other similar mutations to be added to the "complex_mutations.tsv" file and handled in the same way.

[emarinier]

Updated the changelog in 2c7307c.

[apetkau]

Can you merge in the latest development to fix merge conflicts?

[emarinier]

Merge conflict should be resolved now.

[emarinier]

Good catch, as always!

I think the issue was the complex mutation logic always assumed there would be existing results to extend, but sometimes there's no results. I added some logic to catch this.