create select method for Poster class

this will cause a parsing error from xml.Elemtree but the poster will change.

Author: blacktwin

plexapi/media.py

@@ -557,6 +557,11 @@ def _loadData(self, data):
         self.selected = data.attrib.get('selected')
         self.thumb = data.attrib.get('thumb')
 
+    def select(self):
+        key = self._initpath[:-1]
+        data = '%s?url=%s' % (key, compat.quote_plus(self.ratingKey))
+        self._server.query(data, method=self._server._session.put)
+
 
 @utils.registerPlexObject
 class Producer(MediaTag):