Small simplification in getClassLoader(Class,Class).

  - LoaderUtil.getThreadContextClassLoader() will not throw an
  exception.
Doc update regarding how servlet contexts can be named.
Upgrade log call to fatal.
Update ConfigurationFactory.Factory to use TCCL.

  - Prefer use of LoaderUtil.
  - Should help fix issues involving the Log4j ClassLoader and the
  application's ClassLoader being different (e.g., LOG4J2-795).