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.
This adds to Zulip support for a user changing their own email
address.
It's backed by a huge amount of work by Steve Howell on making email
changes actually work from a UI perspective.
Fixes#734.
Lauryn Menard
Vishnu KS
Brock Whittaker
Vishnu Ks
Aditya Bansal
Umair Khan