More changes to MangaDetailActivity and its fragments

app/src/main/java/eu/kanade/mangafeed/data/helpers/DatabaseHelper.java

@@ -57,6 +57,11 @@ public class DatabaseHelper implements MangaManager, ChapterManager {
         return mChapterManager.getChapters(manga);
     }
 
+    @Override
+    public Observable<List<Chapter>> getChapters(long manga_id) {
+        return mChapterManager.getChapters(manga_id);
+    }
+
     @Override
     public Observable<PutResult> insertChapter(Chapter chapter) {
         return mChapterManager.insertChapter(chapter);

app/src/main/java/eu/kanade/mangafeed/data/managers/ChapterManager.java

@@ -15,6 +15,8 @@ public interface ChapterManager {
 
     Observable<List<Chapter>> getChapters(Manga manga);
 
+    Observable<List<Chapter>> getChapters(long manga_id);
+
     Observable<PutResult> insertChapter(Chapter chapter);
 
     Observable<PutResults<Chapter>> insertChapters(List<Chapter> chapters);

app/src/main/java/eu/kanade/mangafeed/data/managers/ChapterManagerImpl.java

@@ -38,6 +38,19 @@ public class ChapterManagerImpl extends BaseManager implements ChapterManager {
         return prepareGetChapters(manga).createObservable();
     }
 
+    @Override
+    public Observable<List<Chapter>> getChapters(long manga_id) {
+        return db.get()
+                .listOfObjects(Chapter.class)
+                .withQuery(Query.builder()
+                        .table(ChaptersTable.TABLE)
+                        .where(ChaptersTable.COLUMN_MANGA_ID + "=?")
+                        .whereArgs(manga_id)
+                        .build())
+                .prepare()
+                .createObservable();
+    }
+
     @Override
     public Observable<PutResult> insertChapter(Chapter chapter) {
         return db.put()