Port YAQL from Python to Javascript

In order to make client side App forms validation as easy as possible, we need to evaluate YAQL constraints on fields directly in Javascript client code (and disable/hide/do-whatever-needed fields). This requires YAQL implemented in Javascript. There exists a Jison js-library (http://zaach.github.io/jison/) which provides flex & bison tools in Javascript. Using this library as a replacement for Ply library (python lex & yacc) it should be possible to port YAQL to Javascript.