Pick the first key colset from the shortest (#343)
Pick the first key colset from the shortest (#343)

I chose to sort them O(N Log N) rather than just do
one loop O(N) because we might also want to then
look at the shortest keys and find the one(s) that
are made of int or serial column(s). If it comes to
that, then we might also want to push this into the
ermrestjs API.

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