Added a USaveCancel widget.
UForm and UCheckbox weren't behaving properly, so I've changed them to be more responsive and usable.
Also, UButton now uses a signal called onClicked, which is only fired when the button can actually be clicked!
Fixed a bug caused by saveEnabled not being refreshed properly
Merge pull request #85 from uCtrl/USaveCancel

Added a USaveCancel widget.