Handle invalid constraints

[yochannah]

Invalid constraints should throw an error before reaching the web service and 400ing.

Example:

Invalid constraint:

{:where {:id "BOB"}}

Valid:

    {:where [{:op "="
     :path "Gene.id"
     :value BOB}]}

currently, imcljs merely ignores invalid constraint properties and converts them to <constraint />. This will always 400 in InterMine webservices.