Add a ‘private’ preview email template endpoint

This will make working on the email template easier.

Includes examples of features like lists, headings, blockquotes, etc.

app/main/views/index.py

@@ -1,12 +1,15 @@
 import markdown
 import os
-from flask import (render_template, url_for, redirect, Markup)
+from flask import (render_template, url_for, redirect, Markup, request)
 from app.main import main
+from app import convert_to_boolean
 from flask_login import login_required
 
 from flask.ext.login import current_user
 from mdx_gfm import GithubFlavoredMarkdownExtension
 
+from notifications_utils.renderers import HTMLEmail
+
 
 @main.route('/')
 def index():
@@ -46,6 +49,42 @@ def delivery_and_failure():
     return render_template('views/delivery-and-failure.html')
 
 
+@main.route('/_email')
+def email_template():
+    return HTMLEmail(
+        govuk_banner=convert_to_boolean(request.args.get('govuk_banner', True))
+    )(
+        'Lorem Ipsum is simply dummy text of the printing and typesetting '
+        'industry.\n\nLorem Ipsum has been the industry’s standard dummy '
+        'text ever since the 1500s, when an unknown printer took a galley '
+        'of type and scrambled it to make a type specimen book. '
+        '\n\n'
+        '# History'
+        '\n\n'
+        'It has '
+        'survived not only'
+        '\n'
+        '*five centuries'
+        '\n'
+        '* but also the leap into electronic typesetting'
+        '\n\n'
+        'It was '
+        'popularised in the 1960s with the release of Letraset sheets '
+        'containing Lorem Ipsum passages, and more recently with desktop '
+        'publishing software like Aldus PageMaker including versions of '
+        'Lorem Ipsum.'
+        '\n\n'
+        '^ It is a long established fact that a reader will be distracted '
+        'by the readable content of a page when looking at its layout.'
+        '\n\n'
+        'The point of using Lorem Ipsum is that it has a more-or-less '
+        'normal distribution of letters, as opposed to using ‘Content '
+        'here, content here’, making it look like readable English.'
+        '\n\n\n'
+        'This is an example of an email sent using GOV.UK Notify.'
+    )
+
+
 @main.route('/documentation')
 def documentation():
     curr_dir = os.path.dirname(os.path.realpath(__file__))