Add min-width on video elements

Such that all the player controls are visible.

Fixes #782

// FREEBIE

stylesheets/_conversation.scss

@@ -440,6 +440,7 @@ li.entry .error-icon-container {
     video {
       background: black;
       min-height: 300px;
+      min-width: 240px;
     }
 
     img {

stylesheets/manifest.css

@@ -1063,7 +1063,8 @@ li.entry .error-icon-container {
   .message-container .attachments video,
   .message-list .attachments video {
     background: black;
-    min-height: 300px; }
+    min-height: 300px;
+    min-width: 240px; }
   .message-container .attachments img,
   .message-list .attachments img {
     cursor: pointer; }