Keep the photo cache clean by checking the database for needed photos…

…, then deleting any photos from the cache that are not needed

public/js/main/IndexController.js

@@ -164,6 +164,25 @@ IndexController.prototype._cleanImageCache = function() {
     //
     // Open the 'wittr-content-imgs' cache, and delete any entry
     // that you no longer need.
+    var imagesNeeded = [];
+    var tx = db.transaction('wittrs');
+    return tx.objectStore('wittrs').getAll().then(function(messages) {
+      messages.forEach(function(message) {
+        if (message.photo) {
+          imagesNeeded.push(message.photo);
+        }
+      });
+      return caches.open('wittr-content-imgs');
+    }).then(function(cache) {
+      return cache.keys().then(function (requests) {
+        requests.forEach(function(request) {
+          var url = new URL(request.url);
+          if (!imagesNeeded.includes(url.pathname)) {
+            cache.delete(request);
+          }
+        });
+      });
+    });
   });
 };
 
@@ -191,4 +210,4 @@ IndexController.prototype._onSocketMessage = function(data) {
   });
 
   this._postsView.addPosts(messages);
-};
+};