[bin/morse] Check precisely that morse python version matches blender one

This commit also remove the output of PYTHONPATH, because, in the case
of a bad interpreter version, it triggers an exception, which is not
easy to understand by user.

While here, fix some too much long string, and simplify import dance, as
it can be only configured with python3.2+
[testing] Add some regression test for multiple humans (#308)
[main] Log python path too at the beginning for debugging purpose
[doc] no Internet required

I haz no Webz :-)
[cmake] Include ctest instead of just enable_test

It allows a lot more versatile targets for testing
[doc] Fix a few old statements in basic tutorial
[builder] Fix get_child() to work recursively

This fix broken BarePr2.set_color()
Let users set the Morsy body color

This can be useful we running tutorials with many Morsy instances, one
per user