epass2003: list_files implemented

Listing files on Feitian ePass2003 now works in `opensc-explorer` and `opensc-tool --list-files`. Note that some files are not returned by the card, such as private key files like 3F00/5015/29xx.

BTW is there any documentation on epass2003 proprietary APDU instructions? They are used in the driver's code, but I was unable to find any reference anywhere.