Implemented new parameter processing

Paraeters are now properly prcessed with regard to parameter sets,
default sets, mandatory parameters, and so forth.

Also, the structure is ready for some new features, which aren't implemented, yet:
* Gathering missing mandatory parameters by UI
* Using pipeline input object's properties to bind arguments
* Only allowing the first command of a pipeline to gather missing mandatory arguments
  from UI instead of taking them from pipeline

All provided tests work with this new structure, even some that have been explicit before.