move database.third_parties models into separate apps

[jacksund]

this is only a proposed move right now and it would require a full database reset.

But as datasets are growing (mostly on the molecular side), I'm starting to see that it makes more sense to organize these into apps. For example, the Materials Project database model would be moved into apps.materials_project.models and its name in the database would become materials_project_structures (plus other tables like materials_project_bandstuctures) instead of data_explorer_materialsproject