[misc/player] Introduce output ability to announce supported formats

Also introduce default output format and selected device format, should the
user want another format.

As part of this, change enum player_format in player.h to enum media_format in
misc.h so that it is akin to struct media_quality.

Modify json API to support this.

docs/json-api.md

@@ -342,6 +342,7 @@ GET /api/outputs
 | needs_auth_key  | boolean  | `true` if output requires an authorization key (device verification) |
 | volume          | integer  | Volume in percent (0 - 100)               |
 | format          | string   | Stream format                             |
+| supported_formats | array  | Array of formats supported by output      |
 
 **Example**
 
@@ -361,7 +362,8 @@ curl -X GET "http://localhost:3689/api/outputs"
       "requires_auth": false,
       "needs_auth_key": false,
       "volume": 0,
-      "format": "alac"
+      "format": "alac",
+      "supported_formats": [ "alac" ]
     },
     {
       "id": "0",
@@ -372,7 +374,8 @@ curl -X GET "http://localhost:3689/api/outputs"
       "requires_auth": false,
       "needs_auth_key": false,
       "volume": 19,
-      "format": "pcm"
+      "format": "pcm",
+      "supported_formats": [ "pcm" ]
     },
     {
       "id": "100",
@@ -383,7 +386,8 @@ curl -X GET "http://localhost:3689/api/outputs"
       "requires_auth": false,
       "needs_auth_key": false,
       "volume": 0,
-      "format": "pcm"
+      "format": "pcm",
+      "supported_formats": [ "pcm" ]
     }
   ]
 }
@@ -453,6 +457,7 @@ curl -X GET "http://localhost:3689/api/outputs/0"
   "needs_auth_key": false,
   "volume": 3
   "format": "pcm",
+  "supported_formats": [ "pcm" ]
 }
 ```