Add option for mysql

[sfsinger19103]

Current version works only with postgresql. Flexibility could be achieved entirely within the database module.

• [ ] Change run_time.ini to include all database info -- including sql_flavor parameter -- under a [database] hoarder
• [ ] Make sure system is backwards compatible with old-style run_time.ini files, which had a [postgresql] header and assumed postgresql
• [ ] Document which routines (e.g., probably removing database, which requires closing connections) use postgres-specific and/or mysql-specific code, so that if folks want to add another kind of database they'll be able to tell what exactly they need to update in database module
• [ ] Update user documentation
• [ ] Unit tests

[sfsinger19103]

This might be a good project for someone who already understands sqlalchemy well.

[sfsinger19103]

• [ ] db_pars
• [ ] get_database_names
• [ ] remove_database
• [ ] create_database
• [ ] restore_to_db
• [ ] append_to_composing_reporting_unit_join
• [ ] test_connection_and_tables
• [ ] append_to_composing_reporting_unit_join
• [ ] create_or_reset_db
• [x] sql_alchemy_connect
• [ ] create_db_if_not_ok
• [ ] get_cdf_db_table_names
• [ ] name_from_id_cursor
• [ ] name_from_id
• [ ] name_to_id_cursor
• [ ] name_to_id
• [ ] get_name_field
• [ ] get_reporting_unit_type
• [ ] insert_to_cdf_db
• [ ] table_named_to_avoid_conflict
• [ ] append_id_to_dframe
• [ ] get_column_names
• [ ] add_records_to_selection_table
• [ ] jurisdiction_id_list
• [ ] data_file_list_cursor
• [ ] data_file_list
• [ ] active_vote_types_from_ids
• [ ] active_vote_types
• [ ] remove_record_from_datafile_table
• [ ] remove_vote_counts
• [ ] get_relevant_election
• [ ] get_relevant_contests
• [ ] get_jurisdiction_hierarchy
• [ ] unsummed_vote_counts_with_rollup_subdivision_id
• [ ] get_contest_with_unknown
• [ ] selection_ids_from_candidate_id
• [ ] export_rollup_from_db
• [ ] read_vote_count
• [ ] list_to_id
• [ ] data_file_download
• [ ] data_file_download_cursor
• [ ] is_preliminary_cursor
• [ ] is_preliminary
• [ ] read_external
• [ ] read_external_cursor
• [ ] display_elections
• [ ] display_jurisdictions
• [ ] vote_types_by_juris
• [ ] contest_families_by_juris
• [ ] parents_by_cursor
• [ ] parents
• [ ] get_vote_count_types_cursor
• [ ] get_vote_count_types
• [ ] read_vote_count_nist
• [ ] create_common_data_format_tables
• [ ] create_table
• [ ] add_standard_records
• [x] reset_db -- deleted
• [x] get_params_from_various -- changed header to [database] and added backwards compatibility for [postgresql] header