hidden percent and max information in ProgressBar sample fixes #301

Thought this was the easiest way to fix #301. Tell me what you think.
So I changed the sample so that it shows "Value: indeterminate" instead of "Value: NaN" in this commit https://github.com/tkrugg/deliteful/commit/da10fc5dca844148eeb5f69d9e63ecbafc772123

I also changed percent value to something I think is more consistent. 
It used to be this.position*100, now it's this.value/this.max*100
So now when value is NaN, percent is NaN as well.

I suspect it was done this way to avoid calculating twice value/max. I did the change in a separate commit https://github.com/tkrugg/deliteful/commit/878e15b88375d03957be1e9b729957f086fec1ca so you can merge it if it makes sense.