Closes #39, closes #37, closes #41; Big refactor in engine
Engine has been divided in components:
- Assets: to deal with files
- I18N: to deal with i18n (duh)
- SchemaIO: to read pieces of schema from files
- Factory: to convert schema to engine objects
- SceneViewer: a libgdx actor that  represents a scene
- GameController: controls loading games/scenes and variables
- And finally, Engine, that correctly builds all previous components and manages a Stage

The editor is not working right now. We need to rethink some things.