Added CommandAPI interface

This interface is importing one method "performCommand" in all future commands.
performCommand has the following parameters:
- scanner, Scanner

src/main/java/org/bitbiome/commands/CommandAPI.java

@@ -0,0 +1,8 @@
+package org.bitbiome.commands;
+
+import java.util.Scanner;
+
+public interface CommandAPI {
+    public void performCommand(Scanner scanner, boolean isRunning, String message);
+
+}