These classes seem to have been copy-pasted from other portico pages
when styling was first done in
122dcc9760. With the current styles,
which are just a handful of rules not scoped to a specific page, it
just makes the billing pages look broken.
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.