Require project_id parameter to be valid and specified on /units

[cambro]

We are about to have a big jump in the number of units that have status_code=active, which will make requests for all units inappropriate/unwieldy. It is probably time to require that project_id be specified for all routes that return unit data (which is really probably just /units and /fossils).

[davenquinn]

Yeah I think it probably makes sense to require either a col_id or project_id to be defined

[davenquinn]

We've fixed this with #266. A new core composite project is now the default filter for all API routes. If searching across projects is desired (e.g., finding columns that intersect an area, project_id=all can be specified. This is not yet documented in case it must be changed.