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.
SOCIAL_AUTH_SUBDOMAIN was potentially very confusing when opened by a
user, as it had various Login/Signup buttons as if there was a realm on
it. Instead, we want to display a more informative page to the user
telling them they shouldn't even be there. If possible, we just redirect
them to the realm they most likely came from.
To make this possible, we have to exclude the subdomain from
ROOT_SUBDOMAIN_ALIASES - so that we can give it special behavior.
Alex Vandiver
Lauryn Menard
Khushiyant
Mateusz Mandera