Initial implementation of #143. Compound object implemented, not
implementing supporting processes.
Working on #143. Refactoring of OPMExecutableInstance, changin names to
OPMProcessInstance to make it parallel to OPMObjectInstance.
Renaming OPMExecutableInstance to OPMProcessInstance.
Removing unused imports and clearing other warnings in the code such as
unused variables.
Fixed data transfer from object to objects:
1) when an object is initialized from a constant or from an argument,
the change is propagated to all consuming variables
2) when an object is changed, the changed is propagated recursively to
all consuming variables
Compound objects are created either explicitly using the "Create"
built-in process or implicitly when a part is added to an object that
was not created previously.
I finally think that complex objects work. Closes #143