User login

- Moved blank page from templates to pages.
- Created method in users controller to validate and send login info to
model.
- Created method to grab first row of a DB query.
- Created method to put data into a session.
- Created method in users model to find a user.
- Created method in users model check password and create a user
session.
- Added validation markup to login page.
- Added "for" attribute to all labels.