Adds CSS formatting for `invalid_email.html`.
Uses the `white-box` style because this page is a redirect when
there is an error with the email the user provided during
registration.
Also, updates the text of this page for some grammar errors and
to clarify the language between an invalid email and an email that
is not allowed by the Zulip organization in question.
Finally, makes any references to the `realm_name` also link to
the Zulip organization with 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.
Lauryn Menard
Vishnu Ks