do not open ics within our app

Signed-off-by: tobiasKaminsky <tobias@kaminsky.me>

src/main/java/com/owncloud/android/ui/preview/PreviewTextFragment.java

@@ -477,6 +477,7 @@ public class PreviewTextFragment extends FileFragment implements SearchView.OnQu
         final List<String> unsupportedTypes = new LinkedList<>();
         unsupportedTypes.add("text/richtext");
         unsupportedTypes.add("text/rtf");
+        unsupportedTypes.add("text/calendar");
         unsupportedTypes.add("text/vnd.abc");
         unsupportedTypes.add("text/vnd.fmi.flexstor");
         unsupportedTypes.add("text/vnd.rn-realtext");