New design for Model classes based around strings for specifying different operators and states.
Restored previous Model class interface for backwards compatibility.
Updated SpinOne model to use new Model class design.
Added OptSet argument to Model::op method. Changed MPSt constructor taking InitState argument to get Model reference from initState instead of providing explicitly. Updated sandbox/sample codes and unit tests accordingly.

Conflicts:
	sample/dmrgj1j2.cc
	sandbox/dmrgj1j2.cc
Deprecated but preserved older MPSt InitState constructor for backwards compatibility.
Fixed some compilation errors arising from conflicts with new and old interfaces to Model and InitState.
Added alternative names for SpinOne states and x eigenstates to SpinOne op method.
Finished converting models to new string-based interface. Converted hams/HubbardChain.h to this new usage.
Fixed typo in localmpo unit test.
Merge branch 'stringmod': new interface for Model classes taking string arguments. Old interface still supported for backwards compatibility.