The structure of the .pxo files is now consisted of a JSON-structured metadata part, where all the data that can be stored as text are, and a binary part, that contain all the actual image data for each cel and project brush.
This makes it easier for users to understand the .pxo structure, easier to add more changes without having to check versions for backwards compatibility, easier to be opened by third-party apps and it allows us to make an "Export JSON metadata" option, that will export just the metadata in JSON format, without the binary image data.
It's backwards compatible and .pxo files from as far as v0.5 are still supported.
A Project class contains project-specific data like name, undo_redo, frames, layers, tags and brushes. These variables have been moved from Global. This is the first step towards multiple tab support, where each tab will be a different Project.
Replaces nested Global.animation_tags arrays. Also replaced array.duplicate(true) with looping through the array and creating a new class for each array element, because duplicate(true) does not create new classes, unfortunately, which was causing issues with undo/redo.
ColorAndToolOptions has now the same code for left and right tool options, with more similar refactoring coming soon to places like Canvas and DrawingAlgos
Instead of having 2 variables for left & right nodes, use an array instead. This will help with better looking code, automation and less repetitive code, as seen in ToolButtons.gd. Move related refactoring will follow.
Moved code from Global.gd and Canvas.gd to DrawingAlgos.gd. Will also move the fill_gaps and draw_brush methods of Canvas.gd next. Maybe even refactor the inside of them a bit to make them easier to read.
