Checkstyle: Prevent using junit Assert

[hohwille]

We should have automated support that renders warnings when using ugly and discouraged JUnit asserts. I am fighting against the wind in OASP to get rid of them and new contributors keep on introducing this bad and obsolete style.
We should use checkstyle to render a warning/error if org.junit.Assert is used (junit.framework.Assert already is deprecated):
http://checkstyle.sourceforge.net/config_imports.html#IllegalImport

[hohwille]

Should be addressed with SonarQube quality profile.