Broaden GWT constructor support.

- create constructors only for public classes
- access protected constructors by using an anonymous class

see 0e8fc838d576af722eaa1f37b9d32d8049138566, thanks @hneuer!
Update ComponentType with packedHasWorldConstructor.
Repair GWT support for @Wire on fields.

 - Added Field.getAnnotation stub to GWT emu. (non functional)
 - GWT does not support name parameter on @Wire.
Envelope ReflectionCacheSourceCreator with the general bliss of tabs.
Merge pull request #139 from junkdog/feature-gwt-protected-constructors

Broaden GWT constructor support + few minor GWT related fixes.