Adds CSS formatting for `no_spare_licenses.html`.
Uses the `white-box` style because this page is a redirect when
a user tries to register for a Zulip Cloud organization that does
not have any available licenses for new users.
Updates reference to `realm_name` to be a link to the `realm_uri`.
Adds HTML title elements to templates that extend either `base.html`,
`portico.html` or `portico_signup.html`, and that are not website
portico landing pages that will use the `PAGE_TITLE` variable to set
the HTML title element (see following commit in series).
Also, updates some templates for missing translation tags.
As a general rule, we want the title element (and page content)
translated. Exceptions that are updated in this commit are templates
used in the development environment, analytics templates that are used
by staff and templates related to Zephyr.