Builds the object table for each RDDL type.

def _build_object_table(self):
        '''Builds the object table for each RDDL type.'''
        types = self.domain.types
        objects = dict(self.non_fluents.objects)
        self.object_table = dict()
        for name, value in self.domain.types:
            if value == 'object':
                objs = objects[name]
                idx = { obj: i for i, obj in enumerate(objs) }
                self.object_table[name] = {
                    'size': len(objs),
                    'idx': idx,
                    'objects': objs
                }