Added ValidableQuestion

With ValidableQuestion you can do things like:

~~~
$question = new ValidableQuestion("Give me something: ", ["required"]);
~~~
or
~~~
$question = new ValidableQuestion("Give me a number: ", ["numeric"]);
~~~
I needed to exctract this out and now I share it here. It's just an idea of a functionality that I had to extend into this amazing package. Hope it helps.

Thanks :)