Add smart reply container to all notification templates

This is the first step towards adding smart replies to Android
notifications:

One-pager:  http://go/1p-smart-reply
PRD:        http://go/srn-prd
Mocks:      http://go/p-notifications
Design doc: http://go/srn-design

This patch adds a smart_reply_container LinearLayout to all notification
templates. The container is gone by default, so all notifications should
still look the same.

Bug: 67765414
Test: View several notifications and confirm that they look the same
Change-Id: I28d3d078e3b88f6340713e7457744d8f367a567e