relations: show only once if both forward and reverse names of a relation are identical

[gythaogg]

In the edit view of an entity - new relations can be created by clicking on buttons that show the available relations. It shows the relations in both forward and reverse. For example in Person entity edit view - "is daughter of" "is mother of" will both appear as distinct options even though they represent the same relation type.

When we have the identical text for both forward and reverse, for example "is sibling of", then it would be sufficient to show it only once.