Removed database call from constructor, added @TODO to getLogoutForm().
Removed $database attribute, renamed $dbHandle to $dbh, switched to
using UserConstants in functions, now using Database object in login(),
register(), and updateLastVisit() functions.
Factored out user-related constants from Constants to newly added
UserConstants class.
Addition of rowCount() function, addition of $singleRow boolean
parameter to fetchAll() to allow the return of a single array row.
Addition of include and use statements for UserConstants class.
Addition of 'strange' username test, include and use statements for
UserConstants class. UserController call changed to pass the Database
object.