Render base govuk_template, create development and production builds

TODO: govuk_template directory should be replaced with submodule
of compiled output of our underscore govuk_template.
Add a Gemfile for Sass, update the README
Delete govuk template files
Add underscore templates as govuk template submodule
Trying out new template with hard link and npm
Grunt and templates should work with mustache and node
correct path to base template
Add frontend toolkit as node and remove submodule
Set port to our GDS default of 3057
Set port using a -p option

This is consistent with how we do other languages.
Update README
Convert head template to Mustache
Merge master into build-process-with-template-submodule
Update README for dev environment
Fix stylesheet minification in production builds
Merge pull request #9 from alphagov/build-process-with-template-submodule

Build process with template submodule
Merge master into set-port-with-dash-p
Update README
Merge pull request #10 from alphagov/set-port-with-dash-p

Set port with -p
Monitor changes and auto restart / recompile