Stdlib Mapping

Unification of mapping functions API in stdlib. 
Commits from Zalim on JavaScript to fix map iteration and other cases. 
Filtering on maps removed from generated code and added to manual code - there are no repetitions in implementations. 
Public APIs return types are converted to either return Maps or collections of Pairs instead of collections of Map.Entry. This is because Entry is view into map and doesn't adhere to snapshot semantics.
When map is silently created under the covers, like in groupBy() use LinkedHashMap instead of HashMap to preserve order. 
Fixes in related tests to make them run in JS, split APIs into JVM and platform independent.