Shared and Stage Specific Object Bag

[malicean]

There should be an object collection with Import<T>() and Export<T>(T value) methods, similar to the old kernel system but greatly simplified. There should be one specific to each individual stage, and there should be one that is shared amongst all stages (like how asset loaders are now). This would remove the static requirements from inter-plugin APIs.

[malicean]

Furthermore, object collections should be scoped to mods. Doing otherwise could cause type conflicts between mods, and a conflict is the last thing that a mod-interop feature should allow for. With this in mind, plugins of the mod should get a mutable object bag (has Export<T>(T value)), but everyone else should only get an immutable object bag (does not have Export<T>(T value).