Review usage of React `key`

[shockey]

In several places, we are using array indices as key prop values - it looks like most take the form of key={i} and key={key}.

This affects rendering performance for the entire collection when the collection's order or length changes, and in certain situations can create unexpected rendering results.[1]

We should review all instances of key prop usage, to ensure that we aren't causing any undue trouble for ourselves.

1: "Index as a key is an anti-pattern" by Robin Pokorny