Merge gobject static code into the gi module

Remove gi._gobject._gobject as a separately compiled static module and
move all the files into gi._gi.
Remove dead module initialization macros from "pyglib-python-compat.h"

https://bugzilla.gnome.org/show_bug.cgi?id=712197
Move gobject sub-module Python files into the main gi package

This moves the signalhelper, propertyhelper, and constants Python modules
from gi/_gobject into gi. Keep gi/_gobject/__init__.py around because it is
still needed to maintain the "_PyGObject_API" exposed by pygobject.h. This
allows external modules compiled with prior versions of PyGObject to
continue working with newer versions.

https://bugzilla.gnome.org/show_bug.cgi?id=712197
Merge static PyGLib module into PyGI

Remove gi._glib._glib as a separately compiled module. Move all C files into
pygobject/gi. Remove compilation and use of libpyglib-gi-2.0-python.so as a
shared dependency since we do not distribute header files for it.
Remove unused threading macros.

https://bugzilla.gnome.org/show_bug.cgi?id=712197
Move Python glib options module into gi package

Move gi/_glib/option.py into gi/_option.py. Remove gi/_glib since it is no
longer needed.

https://bugzilla.gnome.org/show_bug.cgi?id=712197