SLING-3148 Merge back from whiteboard/fmeschbe/featureflags/feature-flags

- Removed ResourceHiding and ResourceTypeHiding
- Added ResourceDecorator support
- Added WebConsole plugin
- Added Feature factory configuration support
- Added JavaDoc
- Support non-Sling ExecutionContext
- Porperly register ClientContext filter as Sling filter

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1561994 13f79535-47bb-0310-9956-ffa450edef68