Added data-binding to a bool property

As discussed, I will try to implement a custom binding to a checkbox.

API:
```cs
this.BindCheckBox(ViewModel, x => x.MyProperty, x => x.MyCommand);
```
where MyProperty was a bool and MyCommand was a ReactiveCommand<bool>.

The binding changes would be handled separate to the events (in theory), but exceptions should be propagated through the command rather than you managing the state of the checkbox yourself.

ReactiveCommand has a .ThrownExceptions property which is an observable stream of exceptions so you can handle those things separate to the actual command. If your error handling runs from that, it should make your code simpler. You just need to throw an exception from your command callback.