This function finds the shared source_mat_ids between the source_data and
sample_data, and sample_ids between the sample_data and feature_data objects.
It also reports any ids that are unique to each object.
If passing a qsip_data object as the first argument, no other arguments are
necessary. If a qsip_source_data is given, then the sample_data and feature_data
objects must be given as well.
Additionally, the results of get_shared_ids() might be obtained from the @shared
slot of a qsip_data object. This data can also be "pretty printed" using the
get_unshared_ids(<qsip_data>) function.