add isConnected and connect methods to interface

Author: gregor-j

src/IConnection.php

@@ -36,6 +36,19 @@ public function __construct(IConfig $config);
      */
     public function getId();
 
+    /**
+     * Is connection established?
+     * @return bool
+     */
+    public function isConnected();
+
+    /**
+     * Establish a connection to the configured system.
+     * In case the connection is already open, close it first.
+     * @throws \phpsap\interfaces\exceptions\IConnectionFailedException
+     */
+    public function connect();
+
     /**
      * Send a ping request via an established connection to verify that the
      * connection works.