This will be helpful when refactoring them to use a common template.
No visual changes.
Tested by create email confirmation link and then manipulated it to
get to various states. Force rendered the realm_creation_disabled
template instead of link_malformed template to check it.
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.