Plugin updater dialog: Use index names

Use index names as the key for plugins rather than names from the
plugin zip file, as deprecated plugins sometimes have the same name in
the zip file, but different names in the index.

src/calibre/gui2/dialogs/plugin_updater.py

@@ -185,7 +185,7 @@ class PluginFilterComboBox(QComboBox):
 class DisplayPlugin(object):
 
     def __init__(self, plugin):
-        self.name = plugin['name']
+        self.name = plugin['index_name']
         self.forum_link = plugin['thread_url']
         self.zip_url = SERVER + plugin['file']
         self.installed_version = None