Optimize node processing system

[RobProductions]

Instead of just processing the nodes directly and applying them to all terrains, we could borrow a MapMagic idea and apply a low resolution version to a "draft terrain" that is stored alongside the main one and then disable it once the main object has received the generation data.

[RobProductions]

Time splicing is now working and the preview mode will serve as a replacement for Draft Terrains, toggled manually by the user. One optimization that could be made instead is having each node track if they or an input have changed and need reevaluating. This would allow the processing system to skip processing them if nothing has changed - important for the thumbnail preview system which currently processes every node individually and goes down their entire input chain each time.

To do this, whenever a property or input changes on a node, the node invalidates all output connected nodes.