Network panel bug fixes

[Bastien Nocera <hadess hadess net>]

Hey,

I found yesterday a number of reference and memory leaks in the 
Network Settings panel.

https://bugzilla.gnome.org/show_bug.cgi?id=746411

Any changes to the leaked objects (connection state, configuration, 
etc.) could lead to the Settings panel crashing after closing the 
Network panel has been closed.

I'd like to land those patches for 3.16.0, and will backport them as 
well.

Cheers