Create event management system, added event notifier for community events

Added functionalities to create and manage events, including the creation of necessary database tables, context menus, modals, and scheduling tasks. Introduced `UserToMessageTracker` utility for tracking user messages within modals.

src/main/java/com/alttd/util/UserToMessageTracker.java

@@ -0,0 +1,19 @@
+package com.alttd.util;
+
+import net.dv8tion.jda.api.entities.Message;
+
+import java.util.HashMap;
+
+public class UserToMessageTracker {
+
+    private final HashMap<Long, Message> userToMessageMap = new HashMap<>();
+
+    public synchronized void putMessage(long userId, Message message) {
+        userToMessageMap.put(userId, message);
+    }
+
+    public synchronized Message pullMessage(long userId) {
+        return userToMessageMap.remove(userId);
+    }
+
+}