added pystun as a pip requirement
Progress on openbazaar launcher.

- Gets external IP (UDP: port) using STUN servers.
- Checks if DYLD_LIBRARY_PATH has been set on MacOSX, if not
  gives a warning and tries to ammend by manually loading
  libssl.dylib and libcrypto.dylib if found at `brew --prefix openssl`.
- default configuration values loaded into a dictionary that will
  be used on the rest of the launching script.