Implement DragomeApplication

[czyzby]

See https://github.com/libgdx/libgdx/blob/master/backends/gdx-backends-gwt/src/com/badlogic/gdx/backends/gwt/GwtApplication.java

• [ ] Application configuration class: created, but settings amount might still change.
• [ ] Graphics implementation:. #7.
• [ ] Input implementation. #10
• [x] Net implementation. #6
• [x] Audio implementation. #12
• [ ] Files implementation. #11
• [x] GL20 implementation. #4
• [x] Preferences support.
• [x] Lifecycle events. #8.
• [x] Clipboard. Supported, but will most likely not work on every platform. We might need to look into clipboard libraries if we want to support copy/paste everywhere, not only inside the application.
• [x] Logging. Supported by DragomeLogger implementations, the default one uses console.log.
• [ ] Gradle support. #3.