Update xcodeproj to newest version

This removes xcodeproj's dependency on a native C extension, which
should make _everything_ better. It also fixes some load issues on 10.10
Let users customize Xcode open command

This lets users override the command to open the project. Possible use
cases:

- Open with a beta version of Xcode
- Open with AppCode
- Open the directory with Vim
- Set the config to `false` to disable automatic opening.
Add --no-open command to cli

This flag will disable the automatic project opening after generation
behavior.