refactor(mf-factor): getInfo is complicate with parametrized dynamic properties

[tpoisseau]

There is some history behind it and the fact that on one end I wanted to use 'short' properties names (em and mz) and on the other one a property name that means something (monoisotopicMass and observedMonoisotopicMass).

I think it will be time to make some big refactoring and breaking changes and only keep monoisotopicMass and observedMonoisotopicMass but I need to find the time to do it (a lot of implications).

Originally posted by @lpatiny in #226