Rather than randomly including one or more of <glib.h>,
<glib-object.h>, and <gio/gio.h> everywhere (and forgetting to include
"nm-glib-compat.h" most of the time), rename nm-glib-compat.h to
nm-glib.h, include <gio/gio.h> from there, and then change all .c
files in NM to include "nm-glib.h" rather than including the glib
headers directly.
(Public headers files still have to include the real glib headers,
since nm-glib.h isn't installed...)
Also, remove glib includes from header files that are already
including a base object header file (which must itself already include
the glib headers).
Rather than having NmtEditor need to know that DSL requires a DSL
page, and Ethernet page, and a PPP page, just have the DSL page itself
return multiple sections.
Instead of having NmtEditorPage be a widget itself, have it just be an
object that returns a list of NmtEditorSections, where
NmtEditorSection is a subclass of NmtNewtSection.
(This will be important when adding VPN pages, which will be split up
into multiple sections, but with the different sections needing to
cooperate on updating the NMSettingVpn. This reorganization lets us
have an NMPageVpn containing multiple sections, with the NMPageVpn
object handling the coordination between the sections.)
