Fixing bugs and adding hotkeys

While drawing, I found a few bugs that needed to be resolved.

Fixes

• Fixed an issue with the help menu being offset
• Fixed a crash when adding and removing tracks in succession
• Fixed a the canvas sometimes being invisible when loading a project
• Fixed the color swap using the wrong color
• Fixing color palette not saving/loading with project
  
• Fixed multi-sample flood fill crash
• Fixing brush preview missing on project load
• Fixed brushing and releasing the brush over UI would cause undo/redo not to be set
• Fixed layer options being behind menu bar
• Fixed layer visibility icon being incorrect when drag/drop sorting layers
• Fixed crash that sometimes happened on rectangle select
• Fixed crash that sometimes happened when selection is cleared
• Fixed invisible selection when tapping a single pixel to select it
• Fixed export name not being used for PNG export
• Fixed crash that sometimes happened when serializing history into temp hot-reload projects
• Fixed filled rectangle preview z-sorting
  
• Fixed issue with canvas going outside the bounds of the viewport
• Fixed reference image layout to be horizontal instead of vertical

Features

• Added Shift+Click in brush tool to draw lines
• Added "d" key to swap between black and white colors for painting