[LOG4J2-688] Make org.apache.logging.log4j.core.layout.PatternLayout immutable. Test without using org.apache.logging.log4j.core.layout.PatternLayout.setConversionPattern(String).

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1605510 13f79535-47bb-0310-9956-ffa450edef68
[LOG4J2-688] Make org.apache.logging.log4j.core.layout.PatternLayout immutable. Remove old API and make ivars final.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1605512 13f79535-47bb-0310-9956-ffa450edef68
[LOG4J2-688] Make org.apache.logging.log4j.core.layout.PatternLayout immutable. 

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1605514 13f79535-47bb-0310-9956-ffa450edef68
Remove unused imports.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1605515 13f79535-47bb-0310-9956-ffa450edef68
Remove unused imports. Follow import style guidelines for static imports.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1605516 13f79535-47bb-0310-9956-ffa450edef68