First phase of outputting static data files under a repository tree. [ci skip]

 * pyrseas/cmdargs.py (parse_args): Set config data_path.
 * pyrseas/database.py (Database.to_map): Move mkdir_parents higher so
   that it's available for multiple_files and datacopy.  Set up
   metadata_dir and datacopy under opts, so it's available downstream
   without having to pass them independently.
 * pyrseas/dbobject/__init__.py (DbObjectDict.to_map): Remove
   metadata_dir argument and use opts item instead.
 * pyrseas/dbobject/schema.py ({Schema, SchemaDict}.to_map): Remove
   metadata_dir argument and use opts item instead.
 * pyrseas/dbobject/table.py (Table.data_import,
   ClassDict.data_export): Add 'table.' prefix to file names.
 * pyrseas/testutils.py (DatabaseToMapTestCase): If datacopy in config
   arg, merge the TEST_DIR as files:data_path.
 * tests/dbobject/test_static.py: Add 'table.' prefix to FILE_PATH.
   In test_copy_static_table, expect the file in the corresponding
   schema directory under the repository tree.

Skipping CI since the latter test will only be addressed in the second
phase.