removed dependency on external libaries (OpenMM) in header files

modules/mol/mm/examples/gb_example_traj.dcd

modules/mol/mm/pymod/export_openmm.cc

modules/mol/mm/pymod/export_settings.cc

modules/mol/mm/src/mm_observer.cc

modules/mol/mm/src/mm_observer.hh

modules/mol/mm/src/mm_settings.hh

modules/mol/mm/src/simulation.cc

modules/mol/mm/src/simulation.hh

modules/mol/mm/src/state_extractor.cc

modules/mol/mm/src/state_extractor.hh

modules/mol/mm/src/steep.cc

modules/mol/mm/src/steep.hh

modules/mol/mm/src/system_creator.cc

modules/mol/mm/src/system_creator.hh

modules/mol/mm/src/topology_creator.hh