Add per-mappack suspend/save support with the option for map creators to save progress automatically

[skysometric]

Inspired by the number of people who dropped Retrush when they forgot to save, this PR adds tooling for map creators to add an "autosave" feature to their mappacks via the animation system. Each mappack now has its own suspend file, saved in the saves directory next to the mappacks folder. To maintain backwards compatibility, old mappacks do not autosave unless the creator adds support for it.

• Suspend files are now per-mappack

  • Each is named after its mappack folder
  • Each is saved in the saves directory
  • saves directory matches current mappack directory (mappacks or alesans_entities/mappacks) in case of mappack name collision

• New animation to "save game progress" added to animations list

  • Map creator may call this whenever they wish
  • Option to notify the player when saving
  • Player may still manually save from the pause menu

[skysometric]

Added a new dialog when starting a new game warning the player that doing so will delete save data. When "New Game" is selected, the "Select World" dialog appears. The save is not deleted until a world is selected. Saves are not deleted when loading the game through the editor, online, or other means.

Alesan, WilliamFrog, and I all collectively agreed that saves should be permanent, and the self-destructing suspends discontinued. As such, the collectables requirement has been removed, and the pause menu has been updated to always show the Save Game option.

This satisfies my level of polish for this PR, so I'm opening it for review and merge.