Minor changes to minimum scrollbar height

[akkartik]

On a tablet the scrollbar is often difficult to acquire, so I've increased the minimum height slightly in my app.

[flamendless]

Awesome PR! Thanks for the contribution.

I'll just request one addition, the scrollbar size should also be an optional parameter so users can easily use their preferred size aside from the minimum default

[akkartik]

This doesn't actually do what I thought it did, sorry for the confusion.