SceneMapWidget, model...

This pr adds a SceneMapWidget in the HomeView.

It's not a complete pr, but in order to keep the lines of code at a minimum I've decided to make the pull request at this moment.

***TODO stuff:***

- Improve SceneWidget so they display thumbnails and other scene-related info.
- Better integrate Selection with the SceneWidget.
- Add some basic edition to the selected scene while in the HomeView. Something like the ability to maark the scene as initial, change its name, etc.