Medusa System Added

Read about the medusa system [here](https://nadekobot.readthedocs.io/en/latest/medusa/creating-a-medusa/)

src/NadekoBot/Bot.cs

@@ -147,12 +147,14 @@ public sealed class Bot
                                       typeof(INService),
 
                                       // behaviours
-                                      typeof(IEarlyBehavior),
-                                      typeof(ILateBlocker),
+                                      typeof(IExecOnMessage),
                                       typeof(IInputTransformer),
-                                      typeof(ILateExecutor))
+                                      typeof(IExecPreCommand),
+                                      typeof(IExecPostCommand),
+                                      typeof(IExecNoCommand))
+                                                .WithoutAttribute<DontAddToIocContainerAttribute>()
 #if GLOBAL_NADEKO
-                    .WithoutAttribute<NoPublicBotAttribute>()
+                                                .WithoutAttribute<NoPublicBotAttribute>()
 #endif
                               )
                               .AsSelfWithInterfaces()
@@ -160,8 +162,7 @@ public sealed class Bot
 
         //initialize Services
         Services = svcs.BuildServiceProvider();
-        var exec = Services.GetRequiredService<IBehaviourExecutor>();
-        exec.Initialize();
+        Services.GetRequiredService<IBehaviorHandler>().Initialize();
 
         if (Client.ShardId == 0)
             ApplyConfigMigrations();