Gameplay-specific behaviours

[Anecoz]

Similar to scripts in Unity et. al. but implemented in C++.

Thoughts:

• Behaviour component, specify a name
• The name refers to some interface class that has been registered in the engine (map<name, instance>
• Collect all nodes that a behaviour runs for and run them serially

This means having to copy Behaviours (c++ code) from the editor to the game, but I feel like this might be fine for me.