Second round of refactoring for Experiment class

This merge request replaces !108 (closed).

I have extensively refactored Experiment.cpp moving all peak collection, data, unit cell and integrator member functions into the respective handlers PeakHandler, Datahandler, UnitCellHandler and IntegrationHandler. I found that the private objects of these classes created as members of Experiment were frequently and unexpectedly deleted during runtime, so they are now instantiated as smart pointers, which fixes the difficulty I had with segfaults.

I would appreciate if you could run your own tests when reviewing this merge request, because it substantially changes the interface.