Improved Lua scripting and fixed bugs

Lua Features

• Added value getting functions to input, slider, and checkbox
• Added layer add function
• Added layer select function
• Added layer count function
• Added function to get current layer and canvas indexes
• Added nudging (moving pixels around)
• Added shape drawing
• Added error message popup on bad scripts
• Added clear layer function
• Added get pixel color function
• Added "View->Engine plugins" to menu bar
• Added Lua script installing from drag->drop into window
  
• Added Artist Plugins shortcut to view menu
• Added color->hex conversion in Lua
• Added example of Lua plugin UI generation
• Lua code is now partially sandboxed so that the app is it's own context
  
• Added "Hot Reload Plugins" in settings to force reload from file each time it opens
  
• Added rs_execute in Lua to allow for better control over history undo/redo

Fixes

• Moved lua code to "plugins" folder
• Greatly improved performance of creating multiple canvases in Lua
• Fixed scrolling bug on horizontal panels (eg: animation window)
• Fixed mouse scroll delta reporting from Windows
• Fixed color8 format from AABBGGAA to RRGGBBAA
• Updated security of Lua plugins
  
• Fixed an issue with vertical scroll boxes not working properly
  
• Fixed an issue with vertical scroll boxes scrolling too slowly