Mark Actors meant to travel early so their flag can be written into the snapshot, followed by moving them over all at once at the same time as previously. On finish, destroy any marked Actors to prevent duplication in hubs. Switch to a unique function that does the verification instead of ChangeStatNum and lock out STAT_TRAVELLING entirely since it shouldn't be used for regular gameplay.
Added safety barriers for STAT_STATIC and STAT_TRAVELLING to avoid potential exploits. Properly clear all internal fields pointing towards non-read barriered data and always relink properly when finishing travelling. Moved ZScript callback to after travelling has finished for all Thinkers, that way everything is initialized correctly. Allow arbitrary thinkers (excluding native ones) to be added to the travelling list (for Actors, their positioning will need to be handled by modders). Ensure lights get re-enabled after travelling.
Adds support for client-side Thinkers, Actors, and ACS scripts (ACS uses the existing CLIENTSIDE keyword). These will tick regardless of the network state allowing for localized client handling and are put in their own separate lists so they can't be accidentally accessed by server code. They currently aren't serialized since this would have no meaning for other clients in the game that would get saved. Other logic like the menu, console, HUD, and particles have also been moved to client-side ticking to prevent them from becoming locked up by poor network conditions. Additionally, screenshotting and the automap are now handled immediately instead of having to wait for any game tick to run first, making them free of net lag.
