[Test][UI] Create a new Scene

Tasks:
- [ ] Create a UI component test for the scene creation flow.
- [ ] Create a test for the injected unity scripts in the scene and editor page.

Currently, the scripts are injected during the loading of the [Preview Component](https://github.com/decentraland/builder/blob/master/src/components/Preview/Preview.tsx#L80) with validation in the [Editor Sagas: renderScene](https://github.com/decentraland/builder/blob/master/src/modules/editor/sagas.ts#L216)