a11y: webclient isn't accessible for screenreader users at all

As a blind user, who depends on a screenreader, I want to be able to use the Keybase interface. Currently, there are so much HTML standards that aren't kept, a link is not an element, things aren't labelled correctly and so on. For me this software isn't usable at all.

Criteria:
* HTML standards are kept
* All links, buttons and elements are clearly labelled
* Compliance with the WCAG 2.0 published by the W3 consortium

The issue does not identify files, tests, or a specific webclient entry point. Begin by locating the webclient interface and auditing its HTML, links, buttons, and labels against WCAG 2.0; done means the interface meets the listed accessibility criteria for screenreader users.

Written by the indexing model from the issue text.