Add support for parallel/multiple active scenes

[ensisoft]

Add support for parallel scenes. Use case, a player character is exploring a map of some sort, the player character enters a building etc. The game should open a new scene that is the interior of the building. This means loading a new scene while keeping the previous scene state. Either keep the previous scene loaded (and either suspend or continue updates) or persist the scene to a temporary storage and load it back later when the next scene ends.

[ensisoft]

Use case for this type of functionality is for example the player character entering a building etc which loads up the interior scene for that building.