This removes the old flex model for the footer to stay at the bottom
of short pages and instead always just positions the footer below
the portico content and makes the content generally tall enough that
issues don't occur.
The check mark which appears for valid input in assorted forms
(such as login and registration) didn't have alternative text
for better accessibility. Added "Valid" as the alt text in all
places it's used.
Fixes#4876.
This completes a major redesign of the Zulip login and registration
pages, making them look much more slick and modern.
Major features include:
* Display of the realm name, description and icon on the login page
and registration pages in the subdomains case.
* Much slicker looking buttons and input fields.
* A new overall style for the exterior of these portico pages.
Brock Whittaker
Vaida Plankyte
Jack Zhang
Rishi Gupta
Harshit Bansal
Jeremy Bowman
Tim Abbott
adnrs96
Vishnu Ks