cubicweb-container #2852503 remove reliance on <clone> rtype [resolved]

The clone code assumes there exists a relation between original and clone and uses this as a trigger to start the actual cloning process.

However not all containers want to maintain such a relation.

prioritynormal
typebug
done in1.0.2
load0.200
load left0.000
closed by#54da8292e68a [entities,tests] give an optional "original" parameter to .clone (closes #2852503)
patch[entities,tests] give an optional "original" parameter to .clone (closes #2852503) [applied]