Propagate colors in split_2step

Reduce the amount of uncolored transitions
after split_2step by trying to color the env transitions.
This is currently only supported for parity like
acceptance conditions.

* spot/twaalgos/game.cc: Determinizatio of "colored"
game can created trivial self-loops. Fix them
* spot/twaalgos/synthesis.cc: Here
* tests/core/ltlsynt.test,
tests/python/_synthesis.ipynb,
tests/python/games.ipynb,
tests/python/synthesis.ipynb,
tests/python/synthesis.py: New and adjusted tests

tests/python/_synthesis.ipynb

@@ -8,7 +8,8 @@
    "outputs": [],
    "source": [
     "import spot, buddy\n",
-    "spot.setup()"
+    "spot.setup()\n",
+    "from spot.jupyter import display_inline"
    ]
   },
   {