Set query and fetch executors to low priority again

app/src/main/java/eu/faircode/email/DB.java

@@ -97,7 +97,7 @@ public abstract class DB extends RoomDatabase {
 
     private static DB sInstance;
     private static ExecutorService executor = Executors.newFixedThreadPool(
-            Runtime.getRuntime().availableProcessors(), Helper.foregroundThreadFactory);
+            Runtime.getRuntime().availableProcessors(), Helper.backgroundThreadFactory);
 
     private static final String DB_NAME = "fairemail";
 

app/src/main/java/eu/faircode/email/ViewModelMessages.java

@@ -47,7 +47,7 @@ public class ViewModelMessages extends ViewModel {
     private AdapterMessage.ViewType last = AdapterMessage.ViewType.UNIFIED;
     private Map<AdapterMessage.ViewType, Model> models = new HashMap<>();
 
-    private ExecutorService executor = Executors.newCachedThreadPool(Helper.foregroundThreadFactory);
+    private ExecutorService executor = Executors.newCachedThreadPool(Helper.backgroundThreadFactory);
 
     private static final int LOCAL_PAGE_SIZE = 100;
     private static final int REMOTE_PAGE_SIZE = 10;