cubicweb-vcwiki #3220109 Have a preview capability in the wiki [validation pending]

so that we do not commit a new version before seeing it

prioritynormal
typeenhancement
done in0.1.0
load0.500
load left0.000
closed by#2cb0f8dcdd55 Add preview functionality to see a modified page before commiting a new revision.
patchAdd preview functionality to see a modified page before commiting a new revision. [applied]