Uuid uniqueness check when building SubGridContainers & JointGridContainer

[johanneshiry]

The current implementations of SubGridContainers and JointGridContainers do not check for uniqueness for uuids by default due to the current implementation of hashCode() and equals(). Hence we cannot ensure, that a Set<> contains unique elements in the sense of a unique uuid.
After discussing how to proceed with this, we agreed not to change the equals() and hashCode() implementations but instead introduce uuid uniqueness checks when building up SubGridContainers & JointGridContainers.