online combination of multiple phrase tables
  - creates a virtual phrase table at decoding time based on a vector of component models and a combination algorithm
  - linear interpolation or instance weighting
  - two possible component model types supported so far: 0 (in-memory) or 12 (compact)
  - weights can be set in config, and overriden on a sentence-level through mosesserver API
  - online optimization (perplexity minimization) using dlib and xmlrpc-c call