WFLY-2681 Send correct content type from management REST API

Also fix some Undertow usage to be more correct/efficent
WFLY-2687 Use VFS based resource loader for deployment overlays
WFLY-2715 Upgrade to PicketBox 4.0.20.Beta4
Remove netty 3.x depandancy
WFLY-2718 Deploying a pure InFlow rar as module drive fail
WFLY-2712 NPE check
cli: addition to fix for https://issues.jboss.org/browse/WFLY-2644 - sync on the list of shutdown handlers to avoid concurrency-related issues