Minor error message formatting fix.
Added no_colorbar option to mutant_positions_and_data.
More methods/properties for Carette mutants; plotting function.

This was done a while ago and not committed!

Refactored Insertional_mutant_Carette method _decide_if_replace_read
method to pull a part out into new _if_confirming_read method.

Added Carette_N_confirming_reads and Carette_N_non_confirming_reads
methods to Insertional_mutant_Carette objects (using _if_confirming_read
method) - TODO need to unit-test!

Added separate get_all_distances function ( Return lists of max
confirmed distances for all mutants and separated into various
categories.) and distance_histogram (Plot histogram of the distances in
the given datasets; optionally save to file.)