libnm: add libnm/libnm-core (part 2)

libnm: add libnm/libnm-core (part 2)

This fixes up the code from the previous "clean" import, and adds
build infrastructure.

[There are two slightly orthogonal sets of changes in this patch.
First, the files added in the previous commit were modified as followed:

  # Replace internal references to "libnm-util" and "libnm-glib" with "libnm"
  perl -pi -e 's/libnm-(util|glib)/libnm/;' libnm-core/*.[ch] libnm-core/tests/*.[ch] libnm/*.[ch] libnm/tests/*.[ch]

  # Fix includes of the enum-types files
  perl -pi -e 's/nm-utils-enum-types/nm-core-enum-types/;' libnm-core/*.[ch] libnm-core/tests/*.[ch] libnm/*.[ch] libnm/tests/*.[ch]
  perl -pi -e 's/nm-glib-enum-types/nm-enum-types/;' libnm/*.[ch] libnm/tests/*.[ch]

  # Fix some python example code
  perl -pi -e 's/import NMClient/import NM/;' -e 's/NMClient.Client\(\)/NM.Client()/;' libnm/nm-client.c

Then, the build infrastructure was added (without further modifying
any existing files in libnm-core or libnm.)

Note: to regenerate libnm.ver after rebase:
  (head -2 libnm-util/libnm-util.ver; (grep -h '\s'nm_ libnm-util/libnm-util.ver libnm-glib/libnm-glib.ver | env LANG=C sort); tail -3 libnm-util/libnm-util.ver) > libnm/libnm.ver
]