yams #5652 change relation declaration in schema [deprecated]

I never liked SubjectRelation and ObjectRelation for I never remember which way they are going. I would like to replace:

class MyEntity(EntityType):

    myrelation = SubjectRelation('OtherEntity')
    otherrelation = ObjectRelation('AnotherEntity')

with something like:

class MyEntity(EntityType):

    myrelation = Relation('self', 'OtherEntity')
    otherrelation = Relation('AnotherEntity','self')

such that it becomes obvious that it means MyEntity myrelation OtherEntity and AnotherEntity otherrelation MyEntity.

done in<not specified>
load left0.000
closed by<not specified>