Add MinimumMass function for lalsimulation's EOS code

The new EOS functionality in lalsimulation is extremely useful. However, it is useful to also know the minimum mass for which the EOS model is defined (yes, this will be O(0.1) solar masses and quite unrealistic, but from a code perspective, we should know the limit).

The necessary data to get that is not currently exposed to python, so I wrote a simple "MinimumMass" function similar to the MaximumMass. This is not as physically meaningful as the former, but does help to know the allowed range of values.