'Get relations between nodes.
Two ways: Source-> Target
Source <- Target'

def getRelations(self):

    for edge in self.edges:
        source = edge.get('source')
        target = edge.get('target')
        if (source not in self.relations):
            self.relations.update({source: [target]})
        if (target not in self.relations):
            self.relations.update({target: [source]})
        values = self.relations[source]
        values.append(target)
        self.relations.update({source: values})
        values = self.relations[target]
        values.append(source)
        self.relations.update({target: values})
