Support app.nw folder on OS X, speeding up app boot

I added a `zip` option, that skips zipping on `OS X` if `false`. It will also avoid generating any zip, if we're only building for `mac` (if building for other platforms it will generate the ZIP file and use it for them).

I've switched this option to `false` by default, since there's no real drawbacks, except a slightly bigger `.app` folder, which is fine since it will probably be distributed through some compressed medium: `.tar.gz`, `.zip` or `.dmg`.

I'll add some quick documentation and example before merging.