Changes url from /help/all-messages to /help/combined-feed.
Also renames files "all-messages.md" and "go-to-all-messages.md"
to "combined-feed.md" and "go-to-combined-feed.md" respectively.
Fixes#27802.
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.
- Adds a new page under the "Reading messages" section documenting
the Inbox view on mobile.
- Adds Inbox, expand more, and expand less SVG mobile icons.
- Cross-links with "Recent conversations" and "All messages".
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.
