models.py:
- refactored the Site/Subject/Project relationships
- Subject now foreign keys directly to Project (not Site)
- Sample now foreign keys directly to Site, in addition to the existing Subject FK, however it's not required (like Visit)
- this affects several templates and views, as well as the decorators and forms

view_project_panels.html:
- don't hide the panels by default, it's annoying to build a panel