Compile problems with example code

I faced some problems with the example code. It seems it is not really up to date. Run a native version with cargo run --release I had to downgrade the egui and eframe dependencies in the editor and example Cargo.toml files to version 0.31.

Trying to compile the web version failed due to the presence of eframe::start_web which had been removed in eframe 0.22 I believe.

I did not manage to upgrade the dependencies correctly, otherwise I would have contributed a PR.