Move LOGGER declarations up class hierarchies to the top and avoid declaring LOGGERs in subclasses. Positive side effect: Remove the static final LOGGER from the Appender interface; IMO interfaces are for contracts, not constants.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1522449 13f79535-47bb-0310-9956-ffa450edef68