PLT 783 Fix Previews for removed YouTube videos (#3073)

* PLT-783 Fix Previews for removed YouTube videos render incorrectly and throw a 404

* Updating video poster for video not found (#3072)

webapp/sass/components/_videos.scss

@@ -10,6 +10,22 @@
         max-width: 100%;
     }
 
+    .video-thumbnail__error {
+        height: 100%;
+        line-height: 2;
+        padding: 110px 0;
+        text-align: center;
+        width: 100%;
+
+        .fa {
+            @include opacity(.5);
+        }
+
+        div {
+            font-size: 1.2em;
+        }
+    }
+
     .block {
         background-color: alpha-color($black, .5);
         border-radius: 10px;
@@ -67,3 +83,7 @@
         height: 500px;
     }
 }
+
+.video-loading {
+    height: 360px;
+}