Structure project builds with Gradle

[AndyMender]

Right now the structure of the repository is very messy with all entrypoint classes located in the root. It would be a good idea to tidy it up and use a build tool like Gradle to generate individual targets. That way it's going to be easier to extend them and build independently.

[AndyMender]

Either at this or later stage, it might be worth combining several classes into a single project based on themes.