Reorganise the main crate and move it to crates/

[somedevfox]

Connections
None

Description
The main crate of Luminol is unnecessarily convoluted. The entry point file (src/main.rs) contains initialisation instructions for both native and web platforms and, consequentially, a lot of #[cfg(target_arch)] macros. They're an eye sore and make the file difficult to navigate at times.

Additionally, when we started the Luminol project, we couldn't initialise the main crate in the crates directory, because one of the dependencies required us to place it into the root directory of the git repository. This is no longer a case, as Trunk can be configured to compile the index.html file in a different directory.

Testing

• Run cargo run and open any project.
• Run trunk run and open any project (in Chromium-based browsers).

Checklist

• Run cargo fmt.
• Run cargo clippy. If applicable, add:
  • --target wasm32-unknown-unknown -Z build-std=std,panic_abort
• Run cargo build --release
• If applicable, run trunk build --release