Atmosphere won't work when packages as self-hosted war

Due to how the org.atmosphere.util.annotation.AnnotationDetector works, classpath scanning for annotations in a file stored in a war fails with an exception (not a file). Extracting the file before launching fixes this.
Add switch to enable atmosphere only when needed.
Merge pull request #433 from AndreasKl/master

Atmosphere won't work when packaged as self-hosted war