[IMPROVEMENT] Improvements in Russian translation

Added translation "Mentions" section.

app/src/main/res/values-uk-rRU/strings.xml

@@ -172,10 +172,9 @@
     <string name="title_members_list">Пользователи</string>
 
     <!-- Mentions -->
-    <!-- TODO Add proper translation-->
-    <string name="msg_mentions">Mentions</string>
-    <string name="msg_no_mention">No mention</string>
-    <string name="msg_all_the_mentions_appear_here">All the mentions\nappear here</string>
+    <string name="msg_mentions">Упоминания</string>
+    <string name="msg_no_mention">Нет упоминаний</string>
+    <string name="msg_all_the_mentions_appear_here">Все упоминания\nотображаются здесь</string>
 
     <!-- Pinned Messages -->
     <string name="title_pinned_messages">Прикрепленные сообщения</string>