z0.6: overview/zoom, new palettes

Updates

• New “Overview” section in the sidebar, showing a minimap view and a moveable zoom area
• New palettes list style
• New palettes: paper-8, retrotronic, toxic-haze, curiosities, pollen8
  • These are based on palettes from lospec.com, but are slightly different since Z-Painter currently fixes the palette size to 10 colors
  • Under the hood, support for downloading and converting any lospec palette exists, but there’s no frontend yet
• Removed the old brush guide (a white stroke in the shape of the brush tip) and replaced with solid, colored guides. This probably requires a bit more iteration
• Some more improvements to brush accuracy. There are still some issues at low resolution though.