UX updates for notif history

- no relative time
- fix background color in dark theme
- fix text alignment in RTL

Test: manual
Bug: 160061165
Bug: 160388261
Bug: 154795795
Change-Id: I7d4c5a5f81ce5b5ce43fdaa3ee99184906753a76

src/com/android/settings/notification/history/NotificationHistoryViewHolder.java

@@ -33,7 +33,6 @@ public class NotificationHistoryViewHolder extends RecyclerView.ViewHolder {
     NotificationHistoryViewHolder(View itemView) {
         super(itemView);
         mTime = itemView.findViewById(R.id.timestamp);
-        mTime.setShowRelativeTime(true);
         mTitle = itemView.findViewById(R.id.title);
         mSummary = itemView.findViewById(R.id.text);
     }