Secondary mass vs. mass ratio

Currently, we have only the secondary mass (m2) specified for pop-syn. But for the first grid (HMS-HMS) we use the mass ratio (q). This causes values to be hard coded instead of being available to the user.

Following the discussions in PRs #271 and #302 we should get an update on the code to consider both m2 and q properly in an equal manner. This need updates in several parts of the code to work simultaneously together to both give the user all options (s)he wants and incorporates it in the structure of our grids.

So we should get rid of all the 0.5/m1 or 0.05*m1 throughout the code and have there the values inferred from the girds by PR #271 and extend them to have always both the q and m2 ranges available.