Reconsider base Convention requirements: location, planting...

Discuss:

1. USDA needs to have a location for entries. This location should be constrained in some way (points, or areas, etc).
2. Right now there is logic in FarmOS to populate location from Assets or movements, etc.
3. Pasa also needs to connect a field (not just a location_)
4. Lastly, Pasa probably will also use plantings to clarify additional activities, as with other groups.
5. We need to decide if we really can have a single Farm Convention... or if we need like two versions... consider require/don't require
   • plant asset (SHOULD not MUST
   • location (on logs) (MUST)

Consider:

1. Always include a 'location' reference, copy from Planting if needed (that's fine)