use ACardEmulator as nfc backend for pcsc-relay

This feature is experimental and disabled by default

At ACardEmulator's compile time it is required:
- to add the correct application identifier to aid_list.xml
- enable the connection to pcsc-relay by setting useVPCD

pcsc-relay/src/pcsc-relay.h

@@ -44,6 +44,7 @@ extern int verbose;
 
 extern struct rf_driver driver_openpicc;
 extern struct rf_driver driver_libnfc;
+extern struct rf_driver driver_vicc;
 
 struct sc_driver {
     int (*connect) (driver_data_t **driver_data);