Update Externals/SFML to 2.1

- all files converted to unix line endings
- files from other subsystems and most of system have been removed
- include/SFML/System.hpp and include/SFML/Network.hpp modified to
  not include removed stuff
- IpAddress.*pp renamed to IPAddress.*pp to workaround git apply bug
  with case-only renames
Port dolphin to SFML 2.1
Merge pull request #1522 from jcowgill/sfml-2.1

Update / Port to SFML 2.1