Demeter template update for OEN Pilot

Context

The OEN Pilot us running an Editoria (Ketty V1) instance with the open textbook planner feature. A number of PDF templates were designed specifically for the textbook features. We're excited to have one book near completion -- to get there, we'd like some tweaks to the Demeter template.

Proposal

1. Add support for a back cover page for the PDF.
   • this is relevant to a PDF that us shared digitally (i.e. not intended for print-on-demand use)
   • use same design as front cover page (user adds image to the component which is placed at the full page size)
   • the user has added a custom back matter component type 'back cover'
2. Tweak the running headers to allow more words on one line (see screenshots below)