Improve download manager. Add an option to select the number of threads for downloads.

app/src/main/java/eu/kanade/mangafeed/data/models/Download.java

@@ -0,0 +1,20 @@
+package eu.kanade.mangafeed.data.models;
+
+import java.io.File;
+import java.util.List;
+
+import eu.kanade.mangafeed.sources.base.Source;
+
+public class Download {
+    public Source source;
+    public Manga manga;
+    public Chapter chapter;
+    public List<Page> pages;
+    public File directory;
+
+    public Download(Source source, Manga manga, Chapter chapter) {
+        this.source = source;
+        this.manga = manga;
+        this.chapter = chapter;
+    }
+}