Add image canvas grid in editor
Fix centering canvas grid
Add bitmap image rendering in image editor
Update bitmap after loading selected costume
Add brush cursor
Use viewport-sized canvases for paint editor

This makes higher zoom levels much faster.
Rename script/costume/soundEditor => scripts/costumes/soundsPanel
Rename costumeEditor => costumesPanel
Fix TypeError
Resize panels when they are selected
Use a backing canvas to allow drawing in image editor
Add basic brush tool to image editor
Zoom in on center of viewport
Show costumes panel by default (temporary)
Don't show initial cursor in top-left corner
Make brush lines solid
Fix drawing lines while scrolling
Fix bitmap position when viewport is larger than canvas
Enable image smoothing at small zoom levels
Floor viewport offset