Flash messages and styling.

Add flash messages to root application layout, add colors and styling
for them.
Current user helper.

Helper method to retrieve current user.  Currently does not work as
we don't have working login.
Login page markup.

HTML / CSS for the user login page. (sessions/new)
Extract Javascript validation.

Moved the validation helper functions to a Validate namespace, and moved
both helpers and actual validation functions to validation.js.  Should
make validation of other forms easier.