add MangaTable.lastFetchedAt and ChapterTable.chaptersLastFetchedAt (#431)

* Add lastFetchedAt and chaptersLastFetchedAt columns to manga

* Update lastFetchedAt columns when data are fetched from source

* Add age and chaptersAge fields to MangaDataClass

* Replace two migrations with single migration

server/src/main/kotlin/suwayomi/tachidesk/manga/impl/Chapter.kt

@@ -100,6 +100,10 @@ object Chapter {
                     }
                 }
             }
+
+            MangaTable.update({ MangaTable.id eq mangaId }) {
+                it[MangaTable.chaptersLastFetchedAt] = Instant.now().epochSecond
+            }
         }
 
         // clear any orphaned/duplicate chapters that are in the db but not in `chapterList`