Ability to give custom relation_type for each relation

[ghost]

When working with datasets such as dbpedia and wikidata, you might want to connect entities and properties with relationships defined by uris. So for each relationship requires a different relationship type, although they connect same type of nodes : entities and properties.

To be able to do that we should be able to connect nodes with a parameter relation_type. So if no rel_type is defined in the Relationship definition, we should take this parameter relation_type and create our relationship with this label. In order to do that, I added a new parameter to RelationshipManager's and cardinalilty.One's connect methods.

How does it sound?