Implement split collections

[TorjeAmundsen]

Overview

Currently, premade splits you can add to your preset in the preset editor are only single splits at a time.

I'd like to implement premade splits as a collection instead, since a lot of the time, splits will have prerequisite dummies that should always be fulfilled before the main image. Structuring it this way would allow you to group these prerequisites along with the main split. Premade splits that are currently just a single split will be converted to a collection with 1 single split in it.

This should also implement a change to the preset.json layout where splits are always stored as collections. The layout editor would need to show splits separated by their collection. Letting the user to reorder splits by dragging either the individual splits or the collection would allow for a better UX experience with reordering when splits have defined prerequisites.

Examples

Nabooru Knuckle cutscene skip

Nabooru Knuckle cutscene skip is very common across categories, and will always be the starting cutscene -> Nabooru dying -> Void.
You could handle this my making a premade split group that contains:

• A Kotake/Komue textbox from the cutscene as dummy
• White flash from Nabooru death as dummy
• Full black fade to split

Hookshot

Hookshot has a very specific chain of events that lets you AutoSplit on Hookshot model over head.
The chain would be handled like this:

• Dampé last textbox へへへ dummy
• Black bar sliver inverted split with a 1000ms delay (it's freaky I know)

There are definitely more examples than this, but this just explains the gist of why I want to implement this feature.