cubicweb-container #3084215 make the <container> relation reflexive [not validated]

That would avoid nasty special cases in some parts of the code (e.g. security rules).

priorityimportant
typeenhancement
done in2.4.0
load1.000
load left0.000
closed by#8f804ee46af4 Switch to rdefs to define the container structure, and make the container relation reflexive
patchSwitch to rdefs to define the container structure, and make the container relation reflexive [applied]