Unifaun ERPConnect documentation.

Revision 1.
Adds translation keys for admin configuration form.
PostNord Logistics REST API wrapper.

Pseudo written wrapper due to we still not have received access to the
service.
Fixes preference typo.

I wonder if the actual variable on Unifaun side has fixed typo error?
Correct translation for Swedish keys.
Base preference pane form for Unifaun settings.