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.
This commit renames "default" views to "home" views in the setting
labels, keyboard shortcuts list, help documentation and its urls.
This commit does not do changes in variable and class names, setting
field in database, API docs and changelog.
Fixes part of #27251.
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
Sahil Batra
Lauryn Menard