unified stub impl with mekon api.
Added new valueSet verb which allows us to generate sets from input data. This is handy for defining universes and vector keys.
e.g. allOrders.map(_.name).valueSet().takeF( nameToTradeSourceFunc )
Added support for 'filter' to VectTerm
This required extending the framework to be aware of whether a new vector cell had a consumable value.
i.e. Vector.filter().map() would throw null pointer exceptions from the map stage if a new column yielded filter=false

 Also started moving some of the core interfaces (HasValue) into Java land so that I can use this from other JVM languages beyond scala.

 Some changes to the "types" type aliases to make this feasible to integrate with true Mekon (or any other Environment implementation). i realised that Function, EventSource are mandatory interfaces and I shouldn't rely on some form of compile-time ducktyping to make this backend portable.