Extend gwt reflection cache with method annotations.

Extends the GWT reflection cache to support method annotations. Similar change to the one we made to support annotation on classes.

Added this for @Subscribe event annotation on Systems and Manager methods. I rather not fork the whole reflection cache for artemis-contrib.

NS2D compiles and runs fine with this change, but to be honest have only done superficial testing. Let me know if you want something more solid first.