cubicweb #2249511 handle http session cleanup with TaskManager [in-progress]

For WSGI at least (as etwist do it its way with twisted.internet.task.LoopingCall)

prioritynormal
typeenhancement
done in<not specified>
load0.250
load left0.250
closed by<not specified>
patchweb/application: instantiate the repository outside of CubicWebPublisher (closes #2249511) [applied]