Core infrastructure rework & Implement group and gradient tags

[MewPurPur]

This isn't close to being done, but now is a decent time to post it.

The bulk of this is a rework to how GodSVG's core infrastructure works, though there are some additional functionalities I got onto while doing this stuff.

• AppInfo.gd is now app_info.json (as it's advantageous to have this be easily fetched from other places, like the GodSVG website)
• Issue templates on Github are now .yaml for a better experience
• Implemented "g", "linearGradient", "radialGradient" tags (Resolves Support <linarGradient> natively #56, Resolves Support the <g> tag natively #434)
• DB now holds the propagatability of all known attributes.
• Tags now correctly consider the attribute defaults established by the <svg> tag and underlying <g> tags
• Tags now correctly calculate the accumulated transform from underlying <g> tags
• Tags now hold their own defaults for non-propagatable attributes (as this is an important aspect of the SVG spec). This is necessary to make some attributes with "auto" values not misleading
• DB now holds the types of all known attributes, so that even in unknown tags, they can give utilities (e.g. fill inside a <polygon> tag will now be recognized as a color attribute)
• Added TagRoot for the root svg, and TagSVG which may in the future be used for nested SVGs
• TagRoot no longer needs to self-replace on unknown changes, now the SVG singleton emits the same signals and can be connected to reliably
• Added functionality for tag configuration warnings (e.g. <stop> tags show a configuration warning when placed under anything other than a gradient)
• Added functionality for shape bounding boxes, will be useful in the future for transformation gizmos and maybe other things
• Added XNode class that Tag inherits from, will be useful in the future to avoid destroying other XML nodes (i.e. comment, CDATA, text)
• Implemented attributes of type ID and a corresponding field
• Implemented rudimentary pretty formatting. Sorry for taking so long - I wanted to do it better than this, but I hope having it be just a checkbox without any configurability will be fine for now
• Tweaked some colors. Changed yellow movement indicators to green, to indicate when the operation is right. Orange might be used in the future for invalid operations (e.g., moving a <stop> tag under something that's not a gradient)
• Used the new "Swatch" theme variation for the fake swatch in the palette editor
• Adds a SHORTCUTS_CHANGED notification (Supersedes Add new strings to GodSVG.pot in advance of global menu PR #671)
• Fixes to the order of drawing in the viewport
• Import Warnings dialog no longer repeats itself
• Added completion percentage to the Language button
• Changed all of the app's icons to consistently use width and height and no viewBox
• Added autoformatting setting for not applying autoformatting to pathdata and transform list attributes. Of course, it only holds for typing them out
• Attributes of the root tag are now added to the UI
• Implemented a setting for window title scheme. When I record GodSVG, the window titles would throw off OBS, so at least to me, this will be useful
• Fixes Focusing the elliptical arc radius parameter field when it's negative changes it #801
• Reworked UndoRedo system to be more robust
• Made tag conversion more reliable
• Renamed tags to elements
• Added support for percentages

[Qainguin]

I just downloaded the Action run for Windows and it just crashes on launch. I already cleared all saved files in the appdata folder.

[MewPurPur]

There's more work to be done, can't guarantee that this is stable until I merge it (or even after, I expect some regressions)

Nonetheless thanks for testing! If you know how to run it through a console and get the error message from there, it'd be really helpful. I'll test your setup in a bit.

Edit: I solved some crashes, but I can't reproduce your situation on my Linux...

[MewPurPur]

@Qainguin The PR is more stable now, I'll be doing more testing over the next week before pushing. Could you check again?

[MewPurPur]

Enough testing for now, I've fixed all major regressions that were found.