Add Specify 7 static files system

[grantfitzsimmons]

Specify 7 falls back on Specify 6's static files quite often for establishing defaults throughout the application. This creates a dependence on Specify 6 updates to change basic defaults for discipline-specific form definitions, the list of interaction tables the user can choose from (specify/specify6#1240), and many other important places.

Simple issues like specify/specify6#1230 cannot be resolved without a Specify 6 update which requires major work for both our development team and our users.

When we add new disciplines or want to set new defaults, we need to have the ability to serve static files via Specify 7 rather than relying entirely on Specify 6. If we want to update the default list of interactions or default forms, we should be able to do so easily by having Specify look at that definition first.

[maxpatiiuk]

More details on the specific static files used by Sp7 in this document - https://docs.google.com/document/d/1UMW4ulbTnmbxz_dHnhs2rwwc_SYoAn3R02QZw4elZZc/edit#heading=h.b3sfx2gf0qls