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/messages.js

@@ -193,7 +193,7 @@
         const { expireTimer } = this.get('expirationTimerUpdate');
         return i18n(
           'timerSetTo',
-          Whisper.ExpirationTimerOptions.getAbbreviated(expireTimer)
+          Whisper.ExpirationTimerOptions.getAbbreviated(expireTimer || 0)
         );
       }
       if (this.isKeyChange()) {