Preparations for public host

This commit adds a lot of new features, optimizations and bugfixes to prepare the bot to be hosted publicly. Updates include a prefix changing command, fixes with box generation to prevent softlocks in later levels, and making edits to game messages instead of sending a new message after each update. Smaller optimizations were made as well, such as removing games from the HashMap when a user quits to save memory.

src/main/java/Bot.java

@@ -2,22 +2,38 @@ import net.dv8tion.jda.api.AccountType;
 import net.dv8tion.jda.api.JDABuilder;
 import net.dv8tion.jda.api.OnlineStatus;
 import net.dv8tion.jda.api.entities.Activity;
+import net.dv8tion.jda.api.entities.Guild;
 
 import javax.security.auth.login.LoginException;
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Paths;
+import java.util.HashMap;
 
 public class Bot {
-    static String prefix = "!";
+    static HashMap<Guild, String> prefixes = new HashMap<Guild, String>();
 
     public static void main(String[] args) throws LoginException, IOException {
         JDABuilder builder = new JDABuilder(AccountType.BOT);
         String token = new String(Files.readAllBytes(Paths.get("token.txt")));
         builder.setToken(token);
         builder.setStatus(OnlineStatus.ONLINE);
-        builder.setActivity(Activity.playing("!play to play Sokoban!"));
+        builder.setActivity(Activity.playing("@Sokobot for info!"));
         builder.addEventListeners(new Commands());
         builder.build();
     }
+
+    static void setPrefix(Guild guild, String prefix)
+    {
+        prefixes.put(guild, prefix);
+    }
+
+    static String getPrefix(Guild guild)
+    {
+        if (!prefixes.containsKey(guild))
+        {
+            return "!";
+        }
+        return prefixes.get(guild);
+    }
 }