When the user launches Settings with a panel passed
as argument, the following things happen:
1. The Wi-Fi panel starts loading.
2. The command line arguments are passed and the given
panel is activated.
3. The Wi-Fi panel cancels the loading routine, and
rfkill_proxy_acquired_cb() is called with the GError
set as G_IO_ERROR_CANCELLED.
4. Crash in rfkill_proxy_acquired_cb().
The crash is caused because, when rfkill_proxy_acquired_cb()
is called, the CcWifiPanel instance isn't valid anymore. And
yet, the code tries to cast 'gpointer user_data' to a
CcWifiPanel pointer.
Fix that by only trying to cast anything after parsing the
GError set by the callback.
The glory moment has come. The new Wi-Fi panel is finally
introduced using a different code style from the rest of
the Network panel, since Control Center itself is written
using the GTK+ C code style.
The Wi-Fi panel uses modern GTK+ features like template
classes and new widgets. The files are stored together
with the Network panel so that we can reuse the abstraction
layer that the Network panel has to manage devices.
https://bugzilla.gnome.org/show_bug.cgi?id=784818
