matcher: API and Celery improvements

* Fixes UnicodeDecodeError thrown by impropper encoding.

* Improvements to the way Celery handles errors, traceback receives
  information is piped into the main log.

* RESULT_TYPE 'error' added to utils.py.

* LogQueue class created to emulate Logger object, stores messages in
  a queue so they can be serialised by MessagePack and piped through
  Celery.

* Minor additional fixes to validation (incorrect parameters).

Signed-off-by: Graham R. Armstrong <graham.richard.armstrong@cern.ch>
matcher: use current_app.logger

* Custom logger removed, replaced with child of current_app.logger.

Signed-off-by: Graham R. Armstrong <graham.richard.armstrong@cern.ch>