Update plugins and dependencies to their latest version.
Cleanup: package-app mojo doesn't need dependency resolution.
Add test mojo.

Does almost the same as surefire except:
 * adds a gwt.args system property built from configuration properties
 * fixes appropriate surefire properties (useSystemClassLoader,
   useManifestOnlyJar=false) and adds warnings for others (forkMode)
 * set default includes to **/*Suite.java and **/*SuiteNoBrowser.java
 * add gwt-dev to additionalClasspathElements