cubicweb #3567793 [ajax controller] deprecate "user callback" impl. [validation pending]

It makes use of session_data, and proposes to store function objects in the session_data.

priorityimportant
typeenhancement
done in3.19.0
load0.100
load left0.000
closed by#954765f57fb6 [web/request] clearly mark user_callback-related methods as deprecated, #e8b9a3d23ad9 [web/request] deprecate user_callback
patch[web/request] clearly mark that these are deprecated [applied][js/ajax] deprecate user-callback support [applied]EditRelationMixIn: stop using user_rql_callback [applied][view] Delete dead(?) code from ReloadableMixIn [applied][web/request] deprecate user_callback [applied][doc] undocument user_callback [applied]