* osmo-smdpp: Implement eUICC + EUM certificate signature chain validation
* Move X.509 related code from osmo-smdpp to pySim.esim.x509_cert
* New pySim.esim.x509_cert module for X.509 certificate handling
* commands: Add method to select parent DF ("cd ..")
* cosmetic: Remove extraneous empty lines between spec-section-comment and class
* USIM + ISIM: Specify the services associated with each file
* filesystem: Maintain a 'service' attribute for all files on a card
* pySim-shell: introduce 'apdu' command for sending raw APDU to card
* pySim-shell: export: allow export as JSON instead of hex
* Fix various mistakes around the CardADF <-> CardApplication dualism
* filesystem: fix various issues found by mypy
* filesystem: Avoid GPL header showing up in sphinx autodoc
* Use sphinx for generating documentation
* Add more documentation to the classes/methods