Use govuk_template with new partials for main layout
Adds a build script to update static from govuk_template upstream

- Designed to ensure that static assets and the layout view are coming in from govuk_template upstream
- Refreshes all node modules, then cherry picks from `govuk_template_ejs` into `public`
Sed command for local layout variables
Remove all unnecessary application CSS
Remove `ensure_master` from build.sh

- Can be built from wherever, and shipped to wherever.

Conflicts:
	build.sh
Revert "Remove all unnecessary application CSS"

This reverts commit 296e041da661837214b61fbb3618cc459d774e61.
Merge pull request #29 from alphagov/govuk_template

Use the GOV.UK template