3532: Show badge on conversations tab on new conversations (#3890)

Fixes #3532

(Old PR, now closed: https://github.com/tuskyapp/Tusky/pull/3533)

Listens on new notifications and if a "direct mention" is detected a
badge (red dot) is shown on the conversations tab if present.

I am missing things like this a lot and also big accounts are unhappy
with the usability so far:
https://mastodon.social/@pallenberg/110129889996182814

app/src/main/java/com/keylesspalace/tusky/db/AppDatabase.java

@@ -42,12 +42,13 @@ import java.io.File;
         TimelineAccountEntity.class,
         ConversationEntity.class
     },
-    version = 53,
+    version = 54,
     autoMigrations = {
         @AutoMigration(from = 48, to = 49),
         @AutoMigration(from = 49, to = 50, spec = AppDatabase.MIGRATION_49_50.class),
         @AutoMigration(from = 50, to = 51),
         @AutoMigration(from = 51, to = 52),
+        @AutoMigration(from = 53, to = 54) // hasDirectMessageBadge in AccountEntity
     }
 )
 public abstract class AppDatabase extends RoomDatabase {