change mappings to use SSSOM-compatible format

[graybeal]

Make mapping UI create and recognize SSSOM-compatible mappings.

1. Save in RDF SSSOM-compatible format
2. Recognize existing mappings that are in SSSOM-consistent RDF format
3. Accept SSSOM mapping files in RDF format
4. Consider accepting SSSOM mapping files in other formats
5. If creating the file, put in better metadata
6. Consider unifying mapping and non-mapping file formats, and allow mappings regardless of the existing file format
7. Enable UI to display triples in mapping files, and mappings in 'regular' files (making mappings an option for viewing file)