[player/outputs] Handle multiple quality levels + use rtp_common (WIP!)

* Untie Airtunes stuff further from player and non-Airplay outputs
* Change raop.c to use rtp_common.c (step 1)
* Change heartbeat of player to 100 ticks/sec, since we have untied from
  Airtunes 352 samples per packet (which equals 126 ticks/sec at 44100)

Still a lot to be done in the player, since the rtptime's in it don't
are probably broken.

src/player.h

@@ -7,15 +7,6 @@
 
 #include "db.h"
 
-// AirTunes v2 packet interval in ns */
-// (352 samples/packet * 1e9 ns/s) / 44100 samples/s = 7981859 ns/packet
-#define AIRTUNES_V2_STREAM_PERIOD 7981859
-
-// AirTunes v2 number of samples per packet
-// Probably using this value because 44100/352 and 48000/352 has good 32 byte
-// alignment, which improves performance of some encoders
-#define AIRTUNES_V2_PACKET_SAMPLES  352
-
 // Maximum number of previously played songs that are remembered
 #define MAX_HISTORY_COUNT 20
 
@@ -85,6 +76,9 @@ struct player_history
 int
 player_get_current_pos(uint64_t *pos, struct timespec *ts, int commit);
 
+int
+player_get_time(struct timespec *ts);
+
 int
 player_get_status(struct player_status *status);