Broken translations

[laulaz]

I worked on adding French translations & found some places where translations strings were missing + fixing typos.

I discovered two problems along the way:

• thanksPageOverride field has the same description (label_thankspageoverride_text) as thanksPageOverrideAction field (help_thankspageoverrideaction_text)
• translations in actions_listing.pt & fields_listing.pt don't work anymore. Some of them are in plone.schemaeditor domain but the translations moved to plone domain