[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/db_init.c

@@ -141,7 +141,7 @@
   "   selected       INTEGER NOT NULL,"			\
   "   volume         INTEGER NOT NULL,"			\
   "   name           VARCHAR(255) DEFAULT NULL,"        \
-  "   authkey        VARCHAR(2048) DEFAULT NULL"        \
+  "   auth_key       VARCHAR(2048) DEFAULT NULL"        \
   ");"
 
 #define T_INOTIFY					\