ChecklistItems cannot be deleted after they've been used in an inspection

[DanielCaspers]

Problem
I discovered when working on #34 that a foreign key constraint fails when trying to remove a checklist item that is already in use.

https://user-images.githubusercontent.com/6056563/35773755-e6029ec4-0920-11e8-9569-d64a2eb7bb8d.png

This does not apply to removing canned responses or measurements from a checklistitem. That works just fine.

Workarounds
ChecklistItems can be removed from a checklist using the EditChecklist view ("With the checkboxes"). They will continue to remain in the ChecklistItems view...

To remove them from the ChecklistItem's view requires one to delete all dependent inspectionItems in MySQL (thus removing reporting history), and anything else necessary to satisfy related foreign key relationships.

Possible solutions
Perhaps we can safely invert the foreign key relationship? I don't know if that is safe or a good idea, and it may be an anti-pattern...