Govspeak and CDT style quotes concurrently (#760)

app/views/markup/_blockquote.html.slim

@@ -0,0 +1,4 @@
+.application-notice.info-notice role='note' aria-label='Information'
+  == quote
+
+p= citation

app/views/markup/_quote.html.slim

@@ -1,4 +1,5 @@
-.application-notice.info-notice role='note' aria-label='Information'
-  == quote
+.blockquote-container
+  blockquote.quote
+    == quote
 
-p= citation
+    cite= citation

config/initializers/markdown.rb

@@ -3,7 +3,7 @@
 class CustomPreprocessor < GovukMarkdown::Preprocessor
   # @return [CustomPreprocessor]
   def apply_all
-    inject_inset_text.inject_details.two_thirds.button.external.quote.video
+    inject_inset_text.inject_details.two_thirds.button.external.quote.blockquote.video
   end
 
   # @example
@@ -69,7 +69,7 @@ def external
   #   This is the citation
   #   {/quote}
   #
-  # @return [CustomPreprocessor]
+  # @return [CustomPreprocessor] CDT style
   def quote
     pattern = build_regexp('quote')
     @output = output.gsub(pattern) do
@@ -79,6 +79,21 @@ def quote
     self
   end
 
+  # @example
+  #   {blockquote}
+  #   This is the quote and the citation
+  #   {/blockquote}
+  #
+  # @return [CustomPreprocessor] Govspeak style
+  def blockquote
+    pattern = build_regexp('blockquote')
+    @output = output.gsub(pattern) do
+      quote, citation = split_content Regexp.last_match(1)
+      blockquote_template.render(nil, quote: nested_markdown(quote), citation: citation)
+    end
+    self
+  end
+
   # @example
   #   {video}872080640{/video}
   #
@@ -117,6 +132,11 @@ def quote_template
     @quote_template ||= Slim::Template.new('app/views/markup/_quote.html.slim')
   end
 
+  # @return [Slim::Template]
+  def blockquote_template
+    @blockquote_template ||= Slim::Template.new('app/views/markup/_blockquote.html.slim')
+  end
+
   # @return [Slim::Template]
   def video_template
     @video_template ||= Slim::Template.new('app/views/markup/_video.html.slim')