New HLTResultMT ByteStream decoder algorithm

Changes include:
* implement HLTResultMTByteStreamDecoderAlg and the corresponding tool -> this reentrant algorithm replaces the functionality of Gaudi Converter for BS decoding, since Converters are inherently not compatible with athenaMT
* make the Converter method HLT::HLTResultMTByteStreamCnv::createObj fail when used with a message to use the Alg instead
* allow TriggerEDMDeserialiserAlg to skip events with no payload - this is needed at least for testing our first bytestream files with new HLTResultMT
* rename one of the HLTResultMT::setStatus overload to setErrorCodes because the overload was ambiguous (compilation error when used)
* add the implementation of operator<<(std::ostream&, const HLT::HLTResultMT&) for useful debug printouts
* add MTCalibPebDecisions to the list of serialised collections in MTCalibPeb.py in order to produce some payload
* fix the payload writing in HLT::HLTResultMTByteStreamCnv::createRep (missing reference operator)


Former-commit-id: e03390a9