Messaging: Implement per conversation channels. Update API level to 28.

* Get rid of in-app settings for notifications, replaced by channels features
* Remove all the notification plumbing and dead code

Test: m, manual

Signed-off-by: Luca Stefani <luca.stefani.ge1@gmail.com>
Signed-off-by: Joey <joey@lineageos.org>
Signed-off-by: Danny Baumann <dannybaumann@web.de>
Signed-off-by: Arne Coucheron <arco68@gmail.com>
Signed-off-by: Lyubo <lyubodzhamov@gmail.com>
Change-Id: Idb39ca32751d40b3376934775d2119dd6cc7e297

src/com/android/messaging/widget/WidgetConversationListService.java

@@ -120,10 +120,6 @@ public class WidgetConversationListService extends RemoteViewsService {
                 remoteViews.setTextViewText(R.id.from,
                         boldifyIfUnread(conv.getName(), hasUnreadMessages));
 
-                // Notifications turned off mini-bell icon
-                remoteViews.setViewVisibility(R.id.conversation_notification_bell,
-                        conv.getNotificationEnabled() ? View.GONE : View.VISIBLE);
-
                 // On click intent.
                 final Intent intent = UIIntents.get().getIntentForConversationActivity(mContext,
                         conv.getConversationId(), null /* draft */);