First steps to factory-izing the runtime, allowing for DynJS or Nashorn.
Use an interface for Config, instead of depending on DynJSConfig.

Also, change RuntimeFactory to have static init() methods and return
factory instance types that know how to create both a Runtime and a
Config instance for a given runtime type.
Remove unused imports
Merge branch 'master' into nashorn

Conflicts:
	src/main/java/io/nodyn/Nodyn.java
	src/main/java/io/nodyn/contextify/ContextifyScriptWrap.java
	src/main/java/io/nodyn/runtime/dynjs/DynJSConfig.java
	src/main/javascript/nodyn/bindings/contextify.js
	src/test/javascript/clusterSpec.js
Replace usages of GlobalObject with GlobalContext or JSObject
Move constants to top-level interface