A much better implementation of isRawJSType().
Cleanup of genBuiltinApply calls.
Cleanup: import definitions._ and jsDefinitions._.
Added JSDictionary which is a dictionary "view" of a JS value.

Also comes with Map-like apply() methods on the companion
object to create "literal" dictionaries. Does not generate
good, raw JavaScript code for now, but it works.
Removed scala.js.JavaScriptObject.

It has been completely superseded by the scala.js.JSAny
hierarchy.