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.

Also:

* Clean up constants
* Rename homepage to statistics page
* Remove configuration page