Initial migration of servlet code to log4j-web.

  - Moved classes and tests.
  - Updated Interpolator to reference the new FQCN.
  - Documentation still needs to be updated.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1592395 13f79535-47bb-0310-9956-ffa450edef68