Reformat imports with isort (#3123)

Besides that:
1. Introduce `setup.py isort` for quick check
2. Introduce GH actions to check imports

features/callback2.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python
 
 import sys
+
 with open("data/{0}/{0}_cb.log".format(sys.argv[1]), "a+") as log:
     log.write(" ".join(sys.argv[-3:]) + "\n")