Renaming / Deleting needs to update all references

[jsolis]

Currently, our foreign references use medicine name which can change.

This causes a problem when renaming / deleting a medicine

We'll need to either

1. Update all references (remembering to update any new foreign data trees added down the line)
2. Use userId and medicineId fields which would never change

Also, if an item is renamed / deleted while another user is looking at it, the app crashes because the item is removed from the apps collection and a re-render is triggered.