Fix multiple-gif display in user page (#4364)

Divide media-items to equal width, and hide overlaps.

app/javascript/styles/stream_entries.scss

@@ -263,7 +263,9 @@
     border: medium none;
     display: block;
     flex: 1 1 auto;
+    width: 100%;
     height: 100%;
+    overflow: hidden;
     margin-right: 2px;
 
     &:last-child {