Support for auxiliary data for online unpackers.

Added support for writing auxiliary data to all online unpackers. This is done by extending the return types from a pair to a triplet, with an additional struct which wraps the extra data. Implementing this struct is done at the detector level.

Currently these structs are empty for all detectors except STS. For STS, it contains a vector which stores the "missed event" flags of hit messages. Structures for other detectors can be implemented as needed (support for this was requested several times by different people).

The writing of this extra data is controlled at the module level by an additional boolean parameter in cbm::algo::sts::UnpackPar which is set to false by default. Adding support for this in the YAML files is left for future work. Also left for future work is directing the produced auxiliary data to some place where it can be processed.