First naive implementation of the RayTracerDemo in Java/GWT

The implementation is split into 3 packages (**client**, **shared** and **server**).
The **client** package contains the `GWT` relevant code and the **server** package the pure java code.
The **shared** package contains classes that are shared in both implementations (i.e. Vector3f, etc)

The project is mavenized. To compile both GWT and Java just run `mvn clean compile gwt:compile`

The Java version can be started with `java -cp target/classes/ io.github.timeu.javagwtraytracerdemo.server.App`.

For the GWT version just go into the web folder and run SimpleHTTPServer: `python -m SimpleHTTPServer`.