Merge branch 'feature/border-color' into 'develop'

src/plainui/jinja2/plainui/assemblies.html

src/plainui/jinja2/plainui/assemblies_all.html

src/plainui/jinja2/plainui/assemblies_events.html

src/plainui/jinja2/plainui/assembly.html

src/plainui/jinja2/plainui/board.html

src/plainui/jinja2/plainui/board_edit.html

src/plainui/jinja2/plainui/board_entry.html

src/plainui/jinja2/plainui/board_private.html

src/plainui/jinja2/plainui/ccc_events.html

src/plainui/jinja2/plainui/components/livestream.html

src/plainui/jinja2/plainui/components/markdown.html

src/plainui/jinja2/plainui/components/resourcesbox.html

src/plainui/jinja2/plainui/components/slider.html

src/plainui/jinja2/plainui/components/tagbox.html

src/plainui/jinja2/plainui/components/three_cards.html

src/plainui/jinja2/plainui/conferences.html

src/plainui/jinja2/plainui/dereferrer.html

src/plainui/jinja2/plainui/event.html

src/plainui/jinja2/plainui/fahrplan.html

src/plainui/jinja2/plainui/header.html