Fetch mangas during the update (#729)

* Optionally fetch mangas during the update

The update only fetched the chapter list of a manga but never the manga itself.
Thus, e.g. unless the manga got online fetched via the ui, it would never get recognized if it is completed or not.
This would e.g. prevent the update setting, to not update completed mangas, from working as intended

* Make settings required

server/src/test/resources/server-reference.conf

@@ -21,6 +21,7 @@ server.excludeUnreadChapters = true
 server.excludeNotStarted = true
 server.excludeCompleted = true
 server.globalUpdateInterval = 12
+server.updateMangas = false
 
 # misc
 server.debugLogsEnabled = true