Implements initial user login support

This commit adds initial support for Spring Security with hard coded
users "user" (pass = "password") and "admin" (pass = "admin").
Limits interface elements based on user role

This commit removes all of the TODOs for showing certain UI elements
based on the logged in user's role. It also adds a "signed in as"
section to the header nav along with a logout link.
Adds support for validating a user against the database

This commit adds a custom UserDetailsService that validates passwords
against the applications database.
Adds ability for people to claim their account

This commit adds the feature that allows a person to claim their
account. It is a two step process:

1) Enter your GW2 display name and a unique code
2) Set your password

Genius!