Fixes cowboy_session:expire/1, replaces ossp_uuid with erlang-uuid

- Fixes cowboy_session:expire/1 (for details refer to https://github.com/esl/cowboy_session/commit/ad3138025cff00519e675af19e117e310e7aaf29#commitcomment-8347333)
- Replaces ossp_uuid with the Erlang UUID Module to get rid of NIF-s.