[AB-xxx] adding check in case the modmail thread has been closed, this is needed because in thread mode one could potentially still execute commands

removing some message command implementations
refactoring the way modmail threads are loaded

abstracto-application/abstracto-modules/modmail/modmail-int/src/main/java/dev/sheldan/abstracto/modmail/exception/ModMailThreadClosedException.java

@@ -0,0 +1,22 @@
+
+package dev.sheldan.abstracto.modmail.exception;
+
+import dev.sheldan.abstracto.core.exception.AbstractoRunTimeException;
+import dev.sheldan.abstracto.core.templating.Templatable;
+
+public class ModMailThreadClosedException extends AbstractoRunTimeException implements Templatable {
+
+    public ModMailThreadClosedException() {
+        super("Mod mail thread closed");
+    }
+
+    @Override
+    public String getTemplateName() {
+        return "modmail_thread_closed_exception";
+    }
+
+    @Override
+    public Object getTemplateModel() {
+        return new Object();
+    }
+}