fix tvdb mappings

[winterbird-code]

Two things to consider in this PR:

• Pocket Monsters: Kami to Yobareshi Arceus has a imdb series ID set; as the README only forbids TMDB series IDs I left it in, but I'm not sure if it should really be there.
• Youjo Shachou only has one long episode in TVDB; it looks like they combine all 13 episodes to one, so that's how I mapped it.

AniDB	TVDB/TMDB/IMDB	Notes
https://anidb.net/anime/3184	https://thetvdb.com/index.php?tab=series&id=260116	Add TVDB ID
https://anidb.net/anime/6782	https://thetvdb.com/index.php?tab=series&id=426542	Add TVDB ID
https://anidb.net/anime/7484	https://thetvdb.com/index.php?tab=series&id=426542	Add TVDB ID, fix offset
https://anidb.net/anime/9016	https://thetvdb.com/index.php?tab=series&id=257755	Add Season mapping
https://anidb.net/anime/12718	https://thetvdb.com/index.php?tab=series&id=317829	Add TVDB ID, fix offset
https://anidb.net/anime/12739	https://thetvdb.com/index.php?tab=series&id=333237	Add TVDB ID
https://anidb.net/anime/15626	https://thetvdb.com/index.php?tab=series&id=383488	Add TVDB ID
https://anidb.net/anime/15748	https://thetvdb.com/index.php?tab=series&id=394293	Add TVDB ID, fix weird episode map
https://anidb.net/anime/16599	https://thetvdb.com/index.php?tab=series&id=409490	Add TVDB ID
https://anidb.net/anime/17151	https://thetvdb.com/index.php?tab=series&id=415119	Add TVDB ID

[BrutuZ]

• TMDB has the warning because their IDs are not unique and it caused issues. IMDB in theory "shouldn't" have them but as there are no issues open complaining it broke something I see no harm leaving that one there :P
• Might be worth fixing the TVDB entry instead? 🤔

[winterbird-code]

There we go; hopefully the changes in TVDB will not be reverted :slightly_smiling_face:

I also fixed the season-offset for Furusato Saisei Nippon no Mukashibanashi... Negative numbers are hard :exploding_head: