add JSON configuration (constants within algorithms)

Similar functionality to https://gitlab.cern.ch/lhcb-parallelization/Allen/merge_requests/204 but with configurable constants defined at the algorithm level instead of being in a common header for each sub-detector.

ConfigurationReader has also been extended to allow writing out a JSON file based on the current values of the constants in the configured sequence.

Workaround currently needed to access constants from within cuda algorithms without linker errors (example in SearchByTriplet).