Allow for same term in different tagsets

Currently it is impossible to add a tag with a duplicate term in the name across different tagsets. Example:

Tagset:
Political Interests
With Terms:
Education
Youth
Human Rights

Tagset:
Works in
With Terms:
K-12
Education <--- THIS IS NOT POSSIBLE - because the term 'Education' is already used in previous Tagset

Tagsets should have unique terms within each tagset, but should not be impacted by other tagsets, so we should be able to have the term 'Education' in both tagsets.

Some considerations:

Terms outside of tagsets - should be unique, and we need to make sure that we are still checking that after making changes.

Currently there is a uniqueness constraint in the DB for tag names - this will need to be addressed, and we'll need to coordinate to get the upgrade script to make adjustments..