This helps in previewing how each spritesheet frame will look when it will be imported in Pixelorama. Note that this does not work well with non-square images at the moment.
More specifically, moved scale, crop, invert, desaturate and generate outline code to DrawingAlgos.gd. I am a little worried of DrawingAlgos.gd getting too big though.
Instead of setting the main arrow as a custom cursor every time the cursor gets inside the viewport, set the viewport's default cursor to be the cross, and change the cross's image once in Global.gd
The "Open" option will handle importing of .pxo files and image files from now on. The "ImportSprites" file dialog node and script are scheduled to be deleted too. Importing spritesheets option will return soon. Next thing I'm going to work on is a preview window that will appear when importing image files.
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.
The Canvas is now single node, instead of having multiple canvases for each frame. This should also be a performance optimization, since there are less canvas nodes, so there are less _input() calls. It should also fix a rare Undo/Redo issue with motion drawing and making lines. Could be unstable, needs more testing.
As a side effect, the guides are now the same for all frames, so this should also close #246.
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
