Extract explicit name-spacing to branch in tufts_models

[mark-dce]

The use of explicit vs. default namespaces does not impact any of the other feature requests in T-DIL OR MIRA. Therefore we should extract it out into a feature branch and revert tufts_models to use a version of the object definitions that is compatible with existing data and fixtures.

ACCEPTANCE

• [x] tufts_models has a feature branch to support continued work and evaluation of explicit name-spacing
• [x] tufts_models master branch uses default name-spacing that is compatible with existing Tufts repository data and fixtures

[bmaddy]

The explicit namespacing branch is explicit-namespaces