Altered create_users_table migration - added new columns to table users.

Users now have a description (text field) and a fullname (varchar(255) field).
Several changes.

- Migration create_users_table was adjusted to include authlevel and
rememberToken.
- The concept of an authlevel (authorization level) was introduced. Check
the User model class source code comments for more details.
- Two BlogController methods were added: errorNoAuth and error404. These are
for errors 401 and 404 respectively. Respective views were also added:
blog.unauth and blog.error404.
- A new kind of method in the User model was introduced. They are the methods
starting with "can". Those will be treated automatically as filters (check
app/filters.php, which was also modified).
- File app/filters.php was modified so that all methods in the User model class
starting with "can" yield filters of the same name which checks if the user is
logged in and if a call to that method with the logged in user returns true
on a == comparison. These filters will use blog.unauth template for the
response output.
- Resource 'user' route was broken into individual routes so filtering can
be precisly applied latter.
- 401 and 404 pages were set to be used whenever those errors happen.
- The missing function hook for 404 errors now use the blog.error404 view
template.