ETCH-282 Runtime accepts now log configuration

A new constructor for the EtchRuntime has been added.
It enables the client/server to register a different log appender for
different log levels.
This is especially useful if you e.g. would like to log errors to your console,
but log info and debug messages to a file.

Change-Id: I0952b4019ef8dc9c5a227fa18a60cc3f5e428058

git-svn-id: https://svn.apache.org/repos/asf/etch/trunk@1578866 13f79535-47bb-0310-9956-ffa450edef68