Improve the Image Preview Panel

[ace-dent]

Please consider:

1. Updating preview panel when selecting different images (not just while editing). i.e. clicking on an image will instantly display its preview, so the preview screen always corresponds to the editor screen.
2. Preview should approximate Arduboy screen, so should alway have square pixels, and...
3. Add fixed scaling options (1:1 tiny!?, 2x, 4x, 8x... ?)
4. Right-click on preview panel gives option to export .png image, etc.
5. Add option for different preview backgrounds, default = black, white, grey, check.

[Pharap]

1. Fairly easy to solve.
2. There's two ways to do this. The easy way would be quick to implement, but it would stop the preview image stretching when the window is resized. The hard way means writing another control and manually writing the rendering code (which admittedly would be similar to what the editor control does, but it's still a bit of a faff).
3. There's at least half a dozen different ways to approach this. A slider with fixed options, a set of radio buttons, zoom in and zoom out buttons, scroll wheel, numeric up-down...
4. Allowing a frame to be exported from the preview panel seems redundant.
5. I can vaguely see an argument for this being useful, though I don't think more than three background colours would be necessary.

[ace-dent]

Additionally support repeating tile design, e.g.

• Add checkbox for 'tiled'. Then show 3x3 tiled images in the preview area.
• Consider dimming (lower contrast) for the 8 surrounding tiles, to highlight central main tile design.
• When dividing preview area x & y by 3, ensure calculated pixel scale is integer to avoid antialiasing of the preview tiles.