REVIEW [NX-505] Require explicit bindings for core and plugins

https://issues.sonatype.org/browse/NX-505

This setting can help find broken/incorrect bindings: http://google-guice.googlecode.com/git/latest-api-diffs/3.0/javadoc/com/google/inject/Binder.html#requireExplicitBindings()

Note that this is a second attempt at #539 now that we've moved away from BVal to Hibernate Validator