Fix Conversation page flickers when back

In this page, there are 3 items flickery when back from conversation
page,
 - The summary under priority conversations
 - The summary under non-priority conversations
 - The clear all button under recent conversations

This is because there is no key on these 3 preferences, when preference
screen updated in onResume(), preference screen thought these 3 are new
items, shows an animation for them. Add keys to them to fix.

Bug: 215073227
Fix: 232341970
Test: visual check
Change-Id: I24691cfa89a624c1741786499b47ede87d518d1a