include "object" in getType

[Rezenders]

Return the "object" type in the getType method, as instances could be defined with the object type since it is included by default.

Also, I don´t understand why the following is necessary:

ros2_planning_system/plansys2_pddl_parser/include/plansys2_pddl_parser/Domain.h

Lines 221 to 225 in a797196

	// We need to populate the constants of all supertypes
	while(t->supertype != nullptr) {
	t = t->supertype;
	t->constants.insert(ts[i]);
	}

It basically creates duplicates of the constants for all its supertypes. Is this really needed?

Related to #317