cubicweb-email #4616894 reimplement mboximport to usr rqlcontroler and maybe cwclientlib [validation pending]

prioritynormal
typetask
done in1.11.0
load1.000
load left0.000
closed by#a07f19f1ce70 add cwclientlib-based mbox import script
patchadd cwclientlib-based mbox import script [applied]