Make replying and mediaPlaying controlled

$refs is not a reliable way to deal with child components under
tree threading as it is not reactive, but the children may change at
any time. The only good way seems to be making these states aggregated on
the conversation component.

Ref: tree-threading

src/components/thread_tree/thread_tree.js

@@ -80,6 +80,9 @@ const ThreadTree = {
     },
     toggleCurrentProp (name) {
       this.toggleStatusContentProperty(this.status.id, name)
+    },
+    setCurrentProp (name, newVal) {
+      this.setStatusContentProperty(this.status.id, name)
     }
   }
 }

src/components/thread_tree/thread_tree.vue

@@ -22,9 +22,13 @@
       :controlled-showing-tall="currentProp.showingTall"
       :controlled-expanding-subject="currentProp.expandingSubject"
       :controlled-showing-long-subject="currentProp.showingLongSubject"
+      :controlled-replying="currentProp.replying"
+      :controlled-media-playing="currentProp.mediaPlaying"
       :controlled-toggle-showing-tall="() => toggleCurrentProp('showingTall')"
       :controlled-toggle-expanding-subject="() => toggleCurrentProp('expandingSubject')"
       :controlled-toggle-showing-long-subject="() => toggleCurrentProp('showingLongSubject')"
+      :controlled-toggle-replying="() => toggleCurrentProp('replying')"
+      :controlled-set-media-playing="(newVal) => setCurrentProp('mediaPlaying', newVal)"
       :dive="dive ? () => dive(status.id) : undefined"
 
       @goto="setHighlight"