(+) CTL-135 Added TaskCommand to Catel.MVVM (NET45 only)
(*) Added Command as base class for TaskCommand.
(+) Added base class for generic command classes. Contains protected static services for using in derived classes.
(-) Removed bad check in Command class in CanExecuteChanged {add/remove} methods causes prevention of subscribing to the event in case when can-execute Func<bool> and Func<TCanExecuteParameter,bool> functions are nulls, but there could be other conditions to check can command be executed or not (e.g. AuthenticationProvider check and any other conditions in overridden Command<>.CanExecute method).