refactor!: initial work for cleaning up `ExonGenomicCoordsMapper`

[korikuzma]

Initial work for #224

Notes:

• Cleaned up docstrings / comments / typos / naming
• Remove unused kwargs in transcript_to_genomic_coordinates and genomic_to_transcript_exon_coordinates
• transcript is now required in transcript_to_genomic_coordinates
• genomic_to_transcript_exon_coordinates accepts either chromosome or alt_ac
• Moves methods from UtaDatabase that do not query the database to ExonGenomicCoordsMapper
• UtaDatabase.chr_to_gene_and_accessions renamed to UtaDatabase.get_genes_and_alt_acs and chromosome is now optional