core, chat: upload plugin system: - extented plugin system so it's not only used with main widget. It is also used for upload widgets and can be extended more - plugin file name is used to detect the type: plugin_wid_* for main widgets, plugin_upload_* for upload widget plugins - a new UploadMenu class allows to easily add an upload button which will use loaded plugins - plugin_info can now specify a list of allowed platforms in "platforms" key - file upload in chat has been moved to a plugin

--- a/src/cagou/kv/menu.kv	Sat Dec 24 14:20:49 2016 +0100
+++ b/src/cagou/kv/menu.kv	Sun Dec 25 16:41:21 2016 +0100
@@ -33,3 +33,6 @@
 
 <MainMenu>:
     cancel_handler_widget: self.parent
+
+<UploadMenu>:
+    cancel_handler_widget: self.parent if self.parent else self.orig_parent