[TASK] Replace Smelly NIH with Symfony/Finder

This replaces my smelly NIH implementation with Symfony/Finder including the ability to
include directories with in()
exclude directories with exclude()
include files with with()
filter based on mediaType with ofMediaType()

filename filtering is not implemented, because mediaType filtering uses name() from finder
and I don't know how to do name() && name() (by default it's like an OR: name() || name())
I'm open to suggestions.