Decouple the Code and Entity views

Currently you can see only one of them an entity or a code file. This forces you to navigate back from the code file just to check something in an entity and go all the way back, and vice versa.
Like the separation of the App Preview and the Dashboard, where you can see an entity or a code file, there should be a separation between the Code, Entites, and App preview views so it will be possible to switch between them without losing the entity, code file, or app page* when you want to see the other.

* The app preview has an annoying bug that changes the selected page back to the first page ever created in the app. I didn’t understand yet when exactly this happens because it doesn’t happen all the time but it does happen every now and then.