Feature/download ahead trigger chapter downloads client side (#597)

* Trigger download ahead while reading client side

* Trigger download ahead while reading earlier

Download ahead was only triggered once the chapter got marked as read

* Optionally ignore dupe chapters for download ahead

* Consider current chapters scanlator for dupe check

* Update download ahead related settings

- add new metadata setting for download ahead limit
- previous setting
  - rename
  - update usage (auto download new chapters limit)

* Select chapter to auto delete while reading depending on ignore dupe setting

Currently, the n-th to last chapter always got deleted ignoring if "ignore dupes" setting was enabled or not.

* Only auto delete chapter while reading if it is read

In case not the last read but the n-th to last read chapter should get auto deleted while reading, it currently just got deleted ignoring if it has been read or not.

src/i18n/locale/en.json

@@ -167,6 +167,12 @@
             "include_in_download": "Entries in excluded categories will not be downloaded even if they are also in included categories"
           }
         },
+        "download_limit": {
+          "label": {
+            "description": "Limit the amount of new chapters that are going to get downloaded.",
+            "title": "Chapter download limit"
+          }
+        },
         "label": {
           "ignore_with_unread_chapters": "Ignore automatic chapter downloads for entries with unread chapters",
           "new_chapters": "Download new chapters"
@@ -197,7 +203,6 @@
       "download_ahead": {
         "label": {
           "description": "How many chapters should get downloaded when marking a chapter as read while reading.",
-          "disclaimer": "This limit will also be applied to the automatic download of new chapters during an update",
           "unread_chapters_to_download": "Number of unread chapters to download",
           "value": "{{chapters}} $t(chapter.title)",
           "while_reading": "Auto download while reading"