renamed player.c to player_control.c

Give player.c a better name, meaning that the code is used to control
the player thread.

src/player_thread.c

@@ -17,7 +17,7 @@
  */
 
 #include "player_thread.h"
-#include "player.h"
+#include "player_control.h"
 #include "playerData.h"
 #include "decoder_control.h"
 #include "audio.h"