'Quote message' is a more accurate decription, as this option inserts
the quoted text into whatever message you're composing or editing;
it does not necessarily start a new reply.
Fixes first part of #31953.
Also create dedicated channels and topics sections in sidebar.
Makes 'start a new topic', a section in introduction to topics
page.
Co-authored-by: Prakhar Pratyush <prakhar@zulip.com>
These files are not Jinja2 templates, so there's no reason that they needed
to be inside `templates/zerver`. Moving them to the top level reflects their
importance and also makes it feel nicer to work on editing the help center content,
without it being unnecessary buried deep in the codebase.
