Prepare for Maven release

With Stephen Connolly we prepared a new configuration to release JUnit in Maven.
Discussed in #511.

The secret stuff is in `settings.xml` -moved away from system properties -not specifying mvn profile in command line explicitly (observed by release-plugin).

+ new server ids in settings.xml
+ removed extensions in `pom.xml`due to HTTP does not need wagon extension
+ added release-plugin which does all the stuff while releasing a new release version