Finish "still left to do" items from FixedRoom2D prototype

[MarkOates]

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From https://github.com/allegroflare/allegro_flare/pull/223

Items are:

• Clarified use case of how script commands and script data will be injected or extended into the prototype.
• Support for multiple rooms
• entity_dictionary and script_dictionary need to be soft-coded
• Strategy for saving/loading content
• Clarify the role of audio_controller. Are users expected to send events or command to the audio controller directly?
• Clarify how audio is loaded into the audio_controller
• Choice dialog should have a reveal animation
• Old ScriptRunner commands code need to be removed