Fixes part of #30918.
We don't need `align-self: baseline;` for `fa-envelope` set in
`message_view_header` since this is a different icon and it appears
better without it like other icons.
We also don't need the explicit font-size for switching b/w 14px and
16px mode since `zulip-icon` class takes care of that by default.
Adds description in views styled like stream descriptions also adds a
help center link to the appropriate page at the end of each
description.
Fixes#29769.
Shubham Padia
Karl Stolley
nimishmedatwal