Improve registered commands caching

Discord's API is slow in updating and registering new commands, so we set up a runnable to periodically check.

src/main/java/wtf/beatrice/hidekobot/runnables/CommandsUpdateTask.java

@@ -0,0 +1,25 @@
+package wtf.beatrice.hidekobot.runnables;
+
+import net.dv8tion.jda.api.JDA;
+import wtf.beatrice.hidekobot.Configuration;
+import wtf.beatrice.hidekobot.HidekoBot;
+import wtf.beatrice.hidekobot.utils.Logger;
+
+public class CommandsUpdateTask  implements Runnable {
+
+    private final Logger logger;
+
+    public CommandsUpdateTask()
+    {
+        logger = new Logger(getClass());
+    }
+
+    @Override
+    public void run() {
+        if(Configuration.isVerbose()) logger.log("Refreshing commands cache...");
+        JDA instance = HidekoBot.getAPI();
+        if(instance == null) return;
+        Configuration.setRegisteredCommands(instance.retrieveCommands().complete());
+        if(Configuration.isVerbose()) logger.log("Commands cache refreshed!");
+    }
+}