Revert "Change path to configuration file in tox.ini"

This reverts commit b0e716c7d83228ec45b08e53f56216acbbe244dd.
Revert "Change path to configuration file in Makefile"

This reverts commit b5961367f00b2f1208dc3600f1ff6d63e7b4901a.
Revert "Single configuration file"

This reverts commit 2fa3709503ec3cbf786aa81ddba1760729ed23de, reversing
changes made to 3f270aab6e62e47d329d699abeede8a23c06232e.