feat(upload): avatar and calendar cover via local disk storage.

POST /v1/user/me/avatar and /v1/calendars/:id/cover; GET /v1/media;
UPLOAD_DIR on eventhub-data volume; MIME/size limits.
Refs EventHub/EventHubBack#71
Refs EventHub/EventHubSpec#8

src/swagger/eventhub_trails.erl

@@ -100,6 +100,9 @@ user() ->
     handler_user_studio_bookings,
     handler_user_following,
     handler_user_me,
+    handler_user_avatar,
+    handler_calendar_cover,
+    handler_media,
     handler_user_reviews
   ],
   lists:flatmap(fun trails_from_module/1, Modules).