Include govuk frontend module in Git

[joelanman]

This is a bit unusual, but because Frontend is currently password protected in NPM, including the modules here means:

• we can deploy the prototype kit site
• we can share this version of the kit more easily

The kit itself is private on GitHub, and will be behind a password when we make it available online.

This PR makes an exception in .gitignore for:

• node_modules/@govuk_frontend
• node_modules/sass-mq

and adds them to the repo

[kr8n3r]

in principle i have no issues with thisas either way you have to share at least one of the passwords (npm test or this one or both)

[joelanman]

@igloosi cheers - sorry I just turned on requiring reviews before merge - do you mind approving?

[kr8n3r]

although it's going to cause pain when packages are updated

[joelanman]

that's true - not sure we have an alternative while we're in alpha/private beta