Fix scroll bar and mouse wheel scrolling

[fluxth]

Set singleStep for scroll bars in WebView

• Sets singleStep to 24px, this allows you to scroll using your mouse scroll wheel :^)

Set pageStep for scroll bars in WebView

• This allows PageUp/PageDown keys to scroll 1 viewport size at a time.
• This also fixes the scroll bar drag handle to be a correct length.

[awesomekling]

Sweet :^)