test-actors: Replace Texture with Image content in an Actor.

* configure.ac:
* tests/Makefile.am: Use gdkmm in examples.
* tests/test-actors.cc: Comment out the unused behaviours.
  Replace use the of Texture actor with a regular Actor with an
  Image via Actor::set_content(), using Gdk::Pixbuf to load the
  and interrogate image data.
  This use of ClutterImage is based on this Clutter example:
  https://git.gnome.org/browse/clutter/tree/examples/image-content.c?h=clutter-1.18