feat: support hiding movie thumbnails

[garretaserra]

Added support for hiding movie thumbnails.
As mentioned in #2 I would want to hide thumbnails on movie libraries because I used them for sports (F1) and if the podium or end of race interview gets picked for the thumbnail it spoils the race.
The solution included adding 2 new configurations:

• also_hide_movie_thumbnails
• movie_thumbnail_path

Also hide movie thumbanails enables this new feature without using the already existing hide_thumbnails which would change behaviour for existing users.

Because movies don't have a parent/grandparent thumbnail it needs a default thumbnail to substitute the existing, this is why i created the other configuration which will allow specifying the file to use.
I didn't include a default image to the repo, but this could be added with a cool template to make it easier to use.

In the code the other significant edits where to ensure that parent/grandparent is not accessed directly as it won't exist and raise and error.

[exscape]

Hey! I haven't had much time the past few weeks, but I gave this a quick glance now. I'll test it out and merge it when I can, but so far it looks excellent!

[garretaserra]

I fully understand, take any time you need :)
And let me know if you feel like it would be better to do it through another approach or need help understanding anything.