* fix handling of no banner (and no default banner) on documents:
- don't try to build a banner URL at the top of document
- don't build a mini-banner in cards
* fix compatibility between custom HTML translator and domains creating
new nodes (and their rendering): hook translator via
app.add_translator so app.add_node can do the job correctly: with
html_translator_class the application is not aware of the new HTML
translator and add_node can't add the relevant rendering methods
* add translation for line_block and line (classes not used, point is
just to have a div for each line so "newlines" are kept
Pretty much completely rewritten theme with custom HTML translator and a
few parts of the old theme extracted to their own extensions.
Banner images thought not to be that huge after all, and not worth the
hassle of them living in a different repository.
co-authored with @stefanorigano
Xavier Morel