Accessibility feedback for authentication flow

Addresses issues #62 (closed) #63 (closed) and #64 (closed)

FEATURES:

• make "show/hide password" toggle focusable using only keyboard
• wrap Signup and Profile successful submission message with a div[role="alert"] so that screen readers will announce it
• set role="radiogroup" for Radio component, and pass aria-label to it so that it can be announced by SRs (requires upgrade of antd library)