Refactor sources

scripts/files/__init__.py

-from .copy_helper import copy_tables, copy_segmentation, copy_image_data, copy_misc_data
-from .folders import make_folder_structure
-from .xml_utils import get_h5_path_from_xml, copy_xml_with_abspath, write_simple_xml
-from .xml_utils import copy_xml_with_newpath
+from .copy_helper import (copy_tables, copy_segmentation, copy_image_data,
+                          copy_misc_data, copy_release_folder)
+
 from .bdv_server import make_bdv_server_file
+
+from .folders import make_folder_structure
+
+from .sources import add_image, add_segmentation, add_source
+from .sources import get_image_names, get_segmentation_names, get_source_names