#22: initial tests of FDNT::GLMoment() in the MegaLUT framework

The current installation works with the MegaLUT framework.  The I/F code actually belongs under `megalut/meas/glmomfunc.py` (to be integrated into megalut).

This issue was mostly about debugging, and making the I/F work.
Note that these guys are not properly implemented yet (covered in issue #20).