Added User page

Note: user's join date was omitted because there really isn't that much user info to show, and email seems too personal to show.
- asks user for a username if they're logged in and don't have a username
- username is checked to be 4-30 characters, alphanumeric and unique
- added links to series and unit pages if the user that created it has a username
- added user_name column to user table