Develop protocols for series level metadata in ead files

These fields are hierarchical and could be used to match mods records to ead descriptions. Extracting it requires: 
1. get c01 - c09, walk down series, subseries, and otherlevel
2. get did> unitid , did> unittitle
3. scopecontent > p (one or many)
4. series_type is level attribute
5. 'series_titles':,
6. 'series_numbers':,
7. 'series_types':,
8. 'series_scope_and_content':,