[PAXWEB-549] Concurrency issues with the war extender

Conflicts:
	pax-web-extender-war/src/main/java/org/ops4j/pax/web/extender/war/internal/Activator.java
	pax-web-extender-war/src/main/java/org/ops4j/pax/web/extender/war/internal/WebEventDispatcher.java
	pax-web-extender-war/src/main/java/org/ops4j/pax/web/extender/war/internal/WebXmlObserver.java
	pax-web-extender-war/src/main/java/org/ops4j/pax/web/extender/war/internal/model/WebApp.java
[PAXWEB-548] Pax-web can sometimes be stuck waiting forever for a servlet to initalize

I think the only possibility to have the servlet not being initialised is if the internal jetty server is stopped, which should be cause the loop to wait forever.

Conflicts:
	pax-web-runtime/src/main/java/org/ops4j/pax/web/service/internal/HttpServiceStarted.java
Fix some javadocs

Conflicts:
	pax-web-jetty/src/main/java/org/ops4j/pax/web/service/jetty/internal/JettyServerImpl.java
[PAXWEB-550] Remove superfluous errors when unregistering a web app
[PAXWEB-551] Shutting down web applications does not correctly clean objects
Conflicts:
	pax-web-jetty/src/main/java/org/ops4j/pax/web/service/jetty/internal/Activator.java
	pax-web-jetty/src/main/java/org/ops4j/pax/web/service/jetty/internal/HttpServiceContext.java
	pax-web-jetty/src/main/java/org/ops4j/pax/web/service/jetty/internal/JettyServerWrapper.java
	pax-web-runtime/src/main/java/org/ops4j/pax/web/service/internal/Activator.java
Align slf4j usage
[PAXWEB-552] Make servlet context handler have a more meaningful display name
Conflicts:
	pax-web-extender-war/src/main/java/org/ops4j/pax/web/extender/war/internal/WebAppHttpContext.java
	pax-web-jetty/src/main/java/org/ops4j/pax/web/service/jetty/internal/HttpServiceContext.java