[raop] Add support for Apple TV device verification, required by tvOS 10.2 (fix for issue #377)

- also change how speakers are saved/retrieved from the db
- add generic authorization methods in outputs.c and player.c
- let filescanner read *.verification files (containing PIN)
- configure options to enable and disable, since libsodium is required

src/player.h

@@ -141,6 +141,9 @@ player_device_add(void *device);
 int
 player_device_remove(void *device);
 
+void
+player_raop_verification_kickoff(char **arglist);
+
 struct player_history *
 player_history_get(void);