Improve first launch speed

[stackotter]

The first launch is an important part of the user experience and some of these changes will even speed up other aspects of the app (such as updating and loading new resource packs).

• [ ] Cache registries and resource pack in the background to allow the app to finish loading without waiting for caches to be created (and potentially warn users if they try to quit the app before caching is finished). This will save a significant amount of time because resource pack caching is kinda slow (I think, profiling required).
• [ ] Figure out which zip library is the fastest (unzipping assets can take a while).
• [ ] Potentially preprocess Pixlyzer data into the format Delta Client likes so that no reformatting is required at runtime (the app could just download the preprocessed files from git or something).

[stackotter]

I have changed all of the registries to use ZippyJSON to load the Pixlyzer JSON. However, ZippyJSONDecoder fails to load the Pixlyzer block registry so I had to hardcode that one to use the regular JSONDecoder. Getting it to work properly with ZippyJSONDecoder would likely make it 2 to 3 times faster.

The issue seems to be the SingleOrMultiple type (because of Pixlyzer's weird formatting).

[stackotter]

I'm closing this for now because the first launch is around 45 seconds after my recent optimisations which is definitely acceptable.