* Fix for Cubari API response not containing chapter release_date
Cubari API responses don't contain release_date information when the Cubari source is Imgur.
The minor change made with this commit makes the existence of the release_date json property for the parsing process optional.
* Fix for Cubari volume "null" and cleaned up chapter name generation
If the volume is set to null in the json, it's now recognized as not specified.
Also cleaned up the chapter name concatenation.
* Replace Gson in Foolslide, Wpmangastream, Gigaviewer and Bilibili.
* Replace Gson in Wpmangareader and Cubari.
* Replace Gson in MangaAdventure and NaniScans.
* Fix missing pages at Wpmangastream (closes#7395).
* Replace Gson in Webtoons and WebtoonsTranslate.
