Gdt 201 data type refactor (#136)

* gdt-201-data-type-refactor

Why these changes are being introduced:
* Updating the TIMDEX data model in accordance with ADR 0002-field-for-data-type-form-information.md

How this addresses that need:
*  Remap content_type to the gbl_resourceType_sm value
* Remove gbl_resourceType_sm from get_subjects method
* Update corresponding unit tests

Side effects of this change:
* None

Relevant ticket(s):
* https://mitlibraries.atlassian.net/browse/GDT-201

* Update dependencies