Let SwingNumberWidget listen for mouse wheel events

[imagejan]

This adds mouse wheel scrolling to sliders and scroll bars created with script parameters, e.g.:

#@ int (style="slider", min=0, max=10) a
#@ double (style="slider", min=10, max=20) b
#@ int (style="scroll bar", min=20, max=30) c

Decrease/increase by scrolling is in integer steps, as those UI widgets currently only support int values (while the underlying model as well as the spinner do support floating point decimals as well). See also #31.

[imagejan]

I rebased this over your latest changes, @ctrueden.

[ctrueden]

🖱 🎡 🎚 👍