Disallow fetching from Wikidata disambiguation pages

Close #23

src/NodaWikidataFetcherDisambiguationIsDisallowedException.php

@@ -0,0 +1,27 @@
+<?PHP
+/**
+ * This file contains an exception class to be thrown if a user attempts to load
+ * data from a Wikidata item specifically established for a disambiguation page.
+ *
+ * @file
+ *
+ * @author Joshua Ramon Enslin <joshua@museum-digital.de>
+ */
+declare(strict_types = 1);
+
+/**
+ * Exception class to be thrown if a user attempts to load
+ * data from a Wikidata item specifically established for a disambiguation page.
+ */
+final class NodaWikidataFetcherDisambiguationIsDisallowedException extends MDgenericInvalidInputsException {
+    /**
+     * Error message.
+     *
+     * @return string
+     */
+    public function errorMessage() {
+        //error message
+        return 'Attempted to load a disambiguation page. Please select the specific item you want to fetch to enrich the given entry: ' . $this->getMessage();
+
+    }
+}