Load custom maps by using custom bundles

[paulhobbel]

As @FlashHit found out that custom bundles are loading in just fine, we should move the custom level loader logic to use custom bundles instead. It's faster, results in smaller files (~56kb) and doesn't make the client hang on load. This all should also result in less or no loading in crashes.

There are however some things to be answered:

1. MapEditor maps have to be converted to custom bundles, how do we do that?
2. Once we have the custom bundles, do we even need custom level loader?
3. Rime is written in .NET 6, which means it's cross platform. Is there any way we can automate the bundle creation?