Add: Exception to be thrown if no matching CommandParser is found

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/network/parser/UnknownCommandException.java

@@ -0,0 +1,9 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.network.parser;
+
+/** Exception thrown when the CommandParserDispatcher has no registered handler for the provided 
+ * request */
+public class UnknownCommandException extends RuntimeException{
+    public UnknownCommandException(String message) {
+        super(message);
+    }
+}