cubicweb-container #4197403 make the <container> relation reflexive [done]

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

priorityimportant
typeenhancement
done in2.7.0
load0.000
load left0.000
closed by#8f804ee46af4 Switch to rdefs to define the container structure, and make the container relation reflexive
patchMigration: for each container etype, we must register the "reflexive" container relation [applied]Fix a failing old test, showing a design problem similar to what is exhibited in #3642859. [rejected]Split entities and hooks [rejected]Merge the 2.6 branch into 2.7 [rejected]Switch to rdefs to define the container structure, and make the container relation reflexive [applied]