Only keep project specific prefs in ignore file

As per best practice ... .gitignore file will be a lot more elegant if
it only lists files that are related to the projects. Global ignore file
should keep overall ignores (OS files) & personal prefs like your
personal editor generated files

- https://help.github.com/articles/ignoring-files
- http://augustl.com/blog/2009/global_gitignores/