Don't reveal grain owner ID to non-owners.
Make spk tool more flexible in a few ways.

- Allow alwaysInclude to specify "." to mean "include everything".
- Add flags to "init" to explicitly set the source path and alwaysInclude. Useful for wrappers like meteor-spk which want to set things up in a specific way.
- Bug fixes.
Merge branch 'master' of github.com:sandstorm-io/sandstorm