Right-clicking on column header resulted in this error:
TypeError: could not convert type EventButton to GdkEvent required for parameter 0
The following fixes and cleans up the issue:
- Move the signal creation to the class, using the __gsignals__ dict.
- Replace `Event` with `object` since we are passing an EventButton as
Gtk3 no longer accepts it as an Event.
- Replace deprecated menu `popup()` with `popup_at_pointer()` which also
fixes a critical gdk error when using `popup()`.
GObject.idle_add is deprecated using GLib.idle_add instead
GObject.timeout_add is deprecated using GLib.timeout_add instead
GObject.SIGNAL_RUN_LAST is deprecated; use GObject.SignalFlags.RUN_LAST instead
GObject.GError is deprecated; use GLib.GError instead
GObject.timeout_add is deprecated use GLib.timeout_add instead.
ListStore(str, str) using unicode_literals get_value return utf8.
