Fix typo.
Add login page.

This is adapted from Freetalk. WoT does not have the shortest unique
name to describe an identity that Freetalk does, so full identity ID is
used instead. This page is also intended for use by other WoT-enabled
plugins, and allows specifying a redirect target after successful login
with the redirect-target parameter. See
plugins.WebOfTrust.ui.web.LogInPage for details.
Rename constant to follow conventions.

Should be all caps with underscores.