Possibly declare UI's query as future clojure.spec data format

[petterik]

The big idea of om.next (imo) is that UI's declare their data requirements as data. Datomic's pull pattern syntax was a good way to achieve this. Depending on how clojure.spec decides to express spec's as data (which has been hinted now for a while), we may want to declare our queries in that format to get leverage from all the tools that are built upon that data format.

We could also check the clojure.spec registry whether a query key (root or field) is spec'ed and do validation on it.