Switch supported dev environment to IntelliJ

[andytill]

Before this change, the supported dev environment was eclipse. Eclipse project files are committed to this repo. Eclipse had setup issues like having to manually include the javafx jar to compile, and other annoying problems in the past.

This change moves support from eclipse to IntelliJ which I have found has last issues to initially setup and get started hacking code.

The idea is to make it as easy as possible for newcomers to get started and contribute back.

No project files are stored in the repo, each new setup will require a project import which is very simple with IntelliJ. I have included a run configuration in the root, it doesn't seem possible for the .idea/runConfigurations directory to survive a new import.

There is a new wiki page showing how to setup https://github.com/andytill/erlyberly/wiki/Dev-Environment

[andytill]

@p-kraszewski I'm going to go with this PR for the dev setup, at least for now. I had to revert to using eclipse because I'm not doing enough java to get used to a new IDE.