Get rid of some of the "needed" tests that have now been taken care of.
Some changes to the grid cell system:
- Add methods to Slot and Room to return the items scheduled (all, publicly, and just starting then).
- Add a method to Item to return the public people scheduled on it.
- Separate out grid_cell and grid_cell_public, so that we're calling different methods in the cell.
- Don't fetch all the items or people in the show_grid() view - leave that for each cell.
Add some tests of the grid output.