Add next/previous navigation in modal for media attachments

app/assets/javascripts/components/actions/modal.jsx

@@ -1,10 +1,14 @@
 export const MEDIA_OPEN  = 'MEDIA_OPEN';
 export const MODAL_CLOSE = 'MODAL_CLOSE';
 
-export function openMedia(url) {
+export const MODAL_INDEX_DECREASE = 'MODAL_INDEX_DECREASE';
+export const MODAL_INDEX_INCREASE = 'MODAL_INDEX_INCREASE';
+
+export function openMedia(media, index) {
   return {
     type: MEDIA_OPEN,
-    url: url
+    media,
+    index
   };
 };
 
@@ -13,3 +17,15 @@ export function closeModal() {
     type: MODAL_CLOSE
   };
 };
+
+export function decreaseIndexInModal() {
+  return {
+    type: MODAL_INDEX_DECREASE
+  };
+};
+
+export function increaseIndexInModal() {
+  return {
+    type: MODAL_INDEX_INCREASE
+  };
+};