Renames CSS rule that styles Zulip UI icons in the help center
so that it makes sense to use it regardless of whether we are
documenting a mobile or desktop/web feature.
- Documents the new contextually-aware button since the instructions
now differ depending on whether you're currently in a direct message
view or not.
- Simplifies the new topic instructions by combining the first two
tabs into a single web/desktop tab, with an optional step 2 to
change the destination stream.
Fixes#27159.
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.
David Rosa
Alya Abbott
Lauryn Menard