Add ability to sort library by date added (closes #1287)

(cherry picked from commit 1813dbbf59)

# Conflicts:
#	app/build.gradle
#	app/src/main/java/eu/kanade/tachiyomi/data/database/DbOpenCallback.kt
#	app/src/main/java/eu/kanade/tachiyomi/ui/browse/migration/search/SearchPresenter.kt
#	app/src/main/java/eu/kanade/tachiyomi/ui/browse/source/browse/BrowseSourcePresenter.kt
#	app/src/main/java/eu/kanade/tachiyomi/ui/library/LibraryPresenter.kt
#	app/src/main/java/eu/kanade/tachiyomi/ui/library/LibrarySettingsSheet.kt
#	app/src/main/java/eu/kanade/tachiyomi/ui/library/LibrarySort.kt
#	app/src/main/java/eu/kanade/tachiyomi/ui/manga/chapter/ChaptersPresenter.kt

app/src/main/java/exh/favorites/FavoritesSyncHelper.kt

@@ -339,6 +339,7 @@ class FavoritesSyncHelper(val context: Context) {
 
                 if (manga?.favorite == true) {
                     manga.favorite = false
+                    manga.date_added = 0
                     db.updateMangaFavorite(manga).executeAsBlocking()
                     removedManga += manga
                 }

app/src/main/java/exh/favorites/LocalFavoritesStorage.kt

@@ -8,6 +8,7 @@ import exh.EXH_SOURCE_ID
 import exh.metadata.metadata.EHentaiSearchMetadata
 import io.realm.Realm
 import io.realm.RealmConfiguration
+import java.util.Date
 import uy.kohesive.injekt.injectLazy
 
 class LocalFavoritesStorage {
@@ -41,6 +42,7 @@ class LocalFavoritesStorage {
                         it.fav,
                         it.manga.apply {
                             favorite = true
+                            date_added = Date().time
                         }
                     )
                 }