Added events to WizardPage so it can cancel a page change. Fixed #7.

Also fixed #8, UpdateSettings not called before finish.
Now the onNext and onPrev method recived the current settings.
Added validation to the WizardTest2 class to show how can you use it.
Merge pull request #17 from PhoneixS/validate-fields

Added events to WizardPage so it can cancel a page change. Fixed #7.