QPID-DISPATCH-16: Improve logging for dispatch

Patches provided by Rajith Attapattu on https://issues.apache.org/jira/browse/DISPATCH-16
- separately configurable logging levels for each module.
- config stubs for syslog & file based logging (not yet implemented.)

Made some modifications:

Simplified schema:
- single configuration section "log", to set defaults use "log : { module:DEFAULT, ... }"
- shorter names for configuration items (print_to_stderr->stderr etc.)
- simplified config logic.

Changed correct but unintuitive bit mask logic: bits in mask were levels NOT selected.
- Flipped it around.

Only log ERROR and above before log system is configured. Avoid annoying INFO log
message leakage to stderr.

git-svn-id: https://svn.apache.org/repos/asf/qpid/dispatch/trunk@1594235 13f79535-47bb-0310-9956-ffa450edef68