Currently, the template only checks if, on a given day, all four yeargroups have the same activity, or if Y9/Y10 have the same activity, or if Y11/Y12 have the same activity, and merge them accordingly. This works, but can be a bit ugly sometimes. Horizontal cells should be merged if they have the same activity. Vertical cells should also be merged if possible (e.g. exam week and grad week). I'm not sure which to prioritize yet though.