Added option for priors to be dictionaries
The priors used for the PE may differ between datasets (i.e. distance prior changed for the O4a PE). This MR changes the parser to allow for the mass, spin, and distance priors to be dictionaries. In data_collection
it will now convert these inputs into dicts with the same keys as the datasets in sample-regex
. The prior is now computed as each individual dataset is read in.