Improve integration of the Config class

Use %config table by default for config classes

Add lastModified() method to retrieve the time of last modification for a
configuration key

Add $defaults to the specified on a subclass. The defaults remove the
necessity to specify a default value for each getter method, and, the
defaults are integrated into the array retrieved from getInfo()
Add a minimum validation to the 'int' type
Add error class for automatic error logging
Add a password reset implementation

Uses a seven step procedure:
  1. (user) Fails to login twice or more
  2. Clicks the 'Forgot my password' link on the login form
  3. Submits the username or email address and triggers a password-reset
     email
  4. Clicks the link in the email and is directed back to the reset page
  5. Enters the username or email again and is logged in
  6. Password change is forced, but current password is not required
  7. Password is updated, user can continue the session without
     authenticating again