More spin buttons

[Karl02]

I'd like to suggest to add spin buttons for several number boxes in the settings to make it possible to change them with the mouse:
1) General > Keyboard/Mouse > Scroll value
2) General > Read/Write: Several sub menus
3) Interface: Limit tab caption to
4) Browser > File list > File list > Files smaller than
5) Browser > Thumbnails > Appearance: Sharpen thumbnail, thumbnail width and height
6) View > View: gamma correction and sharpen
7) View > Misc: Slide show delay
8) View > Fullscreen: pixel size

There should be useful step sizes depending on the values, e.g. "1.000", step size "0.1", or using a slider for coarse changes and spin buttons for fine changes "0.001".

Tested with XnView v2.33 (2015-06-18) on Windows 7 64 bit SP1.