Responding to feedback on the updated visuals (#2549)

* Conversation List Item: timestamp bold only when convo has unread

* Preserve the positioning of overlays on re-entry into convo

* ConversationListItem: Handle missing and broken thumbnails

* Shorten timestamp in left pane for better Android consistency

* Update convo last updated if last was expire timer change

But not if it was from a sync instead of from you or from a contact.

* Make links in quotes the same color as the text

* MediaGridItem: Update placeholder icon colors for dark theme

* Ensure turning off timer shows 'Timer set to off' in left pane

* ConversationListItem: Show unread count in blue circle

* Add one pixel margin to blue indicator for text alignment

* Ensure replies to voice message can bet sent successfully

js/models/conversations.js

@@ -207,7 +207,7 @@
         ...this.format(),
 
         lastUpdated: this.get('timestamp'),
-        hasUnread: Boolean(this.get('unreadCount')),
+        unreadCount: this.get('unreadCount') || 0,
         isSelected: this.isSelected,
 
         lastMessage: {
@@ -795,7 +795,9 @@
 
             return {
               contentType,
-              fileName,
+              // Our protos library complains about this field being undefined, so we
+              //   force it to null
+              fileName: fileName || null,
               thumbnail: thumbnail
                 ? {
                     ...(await loadAttachmentData(thumbnail)),