Get rid of duplicated `project.json` in box.rb

[mikeschinkel]

Default project.json should come from wplib/box-scripts not be hardcoded within box.rb.

[MickMake]

Maybe do a simple wget of https://raw.githubusercontent.com/wplib/box-scripts/master/etc/releases/${VERSION}/project.json

[mikeschinkel]

@MickMake wget is not on Mac by default, and curl is not on Windows by default.

Ideally we'd pull it out of the box, if possible, unless there is a chicken-or-egg problem.

Alternately I can hopefully find a Ruby solution that will run inside Vagrant to do an HTTP GET, maybe this.