These changes should be included in bd9b74436c,
as it makes sure that Zulip limited plan realm won't be able to change the
`message_retention_days` setting.
This commit introduces two new functions in 'url_encoding.py' which
centralize two common patterns for constructing redirect URLs. It
also migrates the files using those patterns to use the new
functions.
This adds a new realm_logo field, which is a horizontal-format logo to
be displayed in the top-left corner of the webapp, and any other
places where we might want a wide-format branding of the organization.
Tweaked significantly by tabbott to rebase, fix styling, etc.
Fixing the styling of this feature's loading indicator caused me to
notice the loading indicator for the realm_icon feature was also ugly,
so I fixed that too.
Fixes#7995.