build folders with gulp api instead of execFile

[clkao]

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[clkao]

it seems we can now use liftoff to get a gulp cli instance. but sadly we need to chdir for each instance, so we still need to have standalone processes for each folder (unless we can achieve with zone or something)

cli = new Liftoff name: 'gulp'
cli.launch (-> handleArguments @), {cwd: '/path/to/project', argv._}

• webworker doesn't work - it's also sandboxed in node-webkit env
• child_process spawn still requires a bundled node executable, but it seems to be the best workaround for now.