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.

tests/core/.gitignore

@@ -0,0 +1,70 @@
+acc
+apcollect
+bddprod
+bitvect
+blue_counter
+checkpsl
+checkta
+complement
+consterm
+defs
+.deps
+*.dot
+eltl2tgba
+emptchk
+defs
+equals
+expect
+expldot
+explicit
+explicit2
+explicit3
+explprod
+graph
+genltl
+input
+intvcomp
+intvcmp2
+kind
+length
+.libs
+ikwiad
+ltl2dot
+ltl2text
+ltlmagic
+ltlprod
+ltlrel
+lunabbrev
+Makefile
+Makefile.in
+maskacc
+mixprod
+nequals
+nenoform
+ngraph
+output1
+output2
+parse_print
+powerset
+*.ps
+randltl
+randtgba
+readsat
+readsave
+reduc
+reduceu
+reductau
+reductaustr
+reduccmp
+reductgba
+stdout
+spotlbtt
+syntimpl
+taatgba
+tgbagraph
+tgbaread
+tostring
+tripprod
+tunabbrev
+tunenoform
+unabbrevwm