Better RDAT parsing, mutpos is now a list of position lists

*Also included a fallback behavior when doing hard EM and REEFFIT cannot
find a good contact_prior_factor: we add a littl white noise to the
hidden reactivities. This usually is an issue when the measurements are
very similar.
*Eterna style RDATs can now be read without issued (sequence is made all
of X and sequences mark the mutations, i.e. there is no mutation
annotation)
*clipzeros option now works as intended