Dialogue: Add Dialogue Message Default Scene as a Project Settings Option

[ch0m5]

Description

Setting the scene to use in every Node is cumbersome. On the documentation, the option to change the Default Scene is proposed, but not yet implemented afaik. This issue aims to resolve this.

Implementation ideas

Add an Orchestrator Project Setting which allows the user to set a .tscn as the Default Scene Dialogue Message Nodes use.