Increased version number to 0.0.5-SNAPSHOT
Changed states to store serialized objects, as references to entities might become invalid by moving the head. Error because states do not have a PolybufConfig at their disposal
Moved the config from BranchManager to Engine, since now every engine necessarily needs a config to create and use states. Removed the line from BranchManager that configured the custom MetaState IO. Engine does not register State on its own, and now BranchManager doesn't either.
State now uses the engine's config
Finish fix-action-deserialization
Made the BranchManager.receiveUpdate method callback-based, too. Makes for an easier API
Added a SyncP message for messages exchanged by BranchManagers (specifically the data to be forwarded by SyncCallbacks)
Added a JGroups Receiver that can communicate updates between branch managers
Added an ExtensionRegistry to properly deserialize messages
Finish add-jgroups