Return 400-class error if there is a Lexical error when calling Repository.Query via REST

"We should never return a 500 for anything caused by user input or REST API input"

If Repository.Query is called via REST and the NXQL query parameter is invalid (i.e. it can't be parsed or executed because of a typographical error or a missing keyword) the return code should not be 500 - it would be better if the RC was something in the 400 range.