added IIssueExistsChecker and Issue<producer_Controller for detection of issues

application/core/IIssueExistsChecker.php

@@ -0,0 +1,15 @@
+<?php
+
+/**
+ * Interface defining method to implement for issue producer (from core and extensions)
+ */
+interface IIssueExistsChecker
+{
+	/**
+	 * Checks if an issue exists.
+	 * Classes for checking if a certain issue exists implement this method.
+	 * @param array $params parameters needed for issue detection
+	 * @return object with success(true) if issue exists, success(false) otherwise
+	 */
+	public function checkIfIssueExists($params);
+}