Ensure templates use layouts/govuk to include the gov template

This is in anticaption of further layouts being shared. I can predict
the need for layouts/start, layouts/question, layouts/error and layouts/done
for example.

By having the govuk base template also be imported using
layouts/govuk_template means we keep consistency in how we extend
layouts.

examples/test-app/views/HelloWorld.html

@@ -1,4 +1,4 @@
-{% extends "govuk_template.html" %}
+{% extends "layouts/govuk_template.html" %}
 {% from "patterns/header.njk" import header %}
 
 {% block head -%}

src/sources/govukTemplate.js

@@ -4,7 +4,7 @@ const CopyWebpackPlugin = require('copy-webpack-plugin');
 //Walk the tree to get back to the root of the module
 const root = path.resolve(require.resolve('govuk_template_jinja'), '../../../');
 
-const templates = path.resolve(root, 'views/layouts');
+const templates = path.resolve(root, 'views');
 const assets = path.resolve(root, 'assets');
 const images = path.resolve(root, 'assets/images');
 const javascripts = path.resolve(root, 'assets/javascripts');