{object} -> {Object}
Remove extra semicolons.
Use jQuery’s .empty().
Make nodelist loops O(n) rather than O(n^2).
Specify radix in parseInt to prevent guessing octal.
Canvas was referencing drawing.all_layers and drawing.current_layer.
Both variables now represent Layer instead of group element and should
be considered private.
Moved Layer class to layer.js
New HistoryRecordingService added to help with moving Layer code out of
Canvas. Started using it in Canvas.mergLayer
