Merge the core and python tests in the tests/ directory
* tests/: Rename as... * tests/core/: ... this. * python/tests/: Rename as... * tests/python/: ... this. * python/tests/run.in: Move as... * tests/run.in: This, and adjust. * tests/Makefile.am: Adjust to run both core and python tests. * configure.ac, README, debian/python3-spot.examples, debian/rules, doc/org/tut.org, python/Makefile.am, spot/ltsmin/Makefile.am, spot/ltsmin/kripke.test, spot/sanity/ipynb.test: Adjust.