Introduce new lockstep syncing system, modularize sync modes (#178)

* Start work on modular sync systems

* Add experimental lockstep sync system, close #69

* Refactor RedisMessageType enum

* Fixup lockstep syncing

* Bump to 3.1

* Update docs with details about the new Sync Modes

* Sync mode config key is `mode` instead of `type`

* Add server to data snapshot overview

* API: Add API for setting data syncers

* Fixup weird statistic matching logic

common/src/main/java/net/william278/husksync/user/OnlineUser.java

@@ -158,7 +158,7 @@ public abstract class OnlineUser extends User implements CommandUser, UserDataHo
             }
             plugin.fireEvent(
                     plugin.getSyncCompleteEvent(this),
-                    (event) -> plugin.getLockedPlayers().remove(getUuid())
+                    (event) -> plugin.unlockPlayer(getUuid())
             );
         } else {
             cause.getFailedLocale(plugin).ifPresent(this::sendMessage);