Merge branch 'syntax_highlight_diff_email' into 'master'

Add syntax colors to diffs in email-on-push notifications

## What does this MR do?
This MR adds syntaxhighlighting to the email-on-push notifications.
## Are there points in the code the reviewer needs to double check?
No
## Why was this MR needed?
Currently the diff in email-on-push notifications is just a monochrome diff that's hard to read.
This MR adds colored syntaxhighlighting to the mails.
## What are the relevant issue numbers / Feature requests?
* It closes https://github.com/gitlabhq/gitlabhq/issues/6994
* There is a Discussion in the Feedback Forum: http://feedback.gitlab.com/forums/176466-general/suggestions/5802256-add-color-to-diffs-in-email-on-push-service-to-htm
* A pull request for this already existed, but was closed. https://github.com/gitlabhq/gitlabhq/pull/7739

## Screenshots
see prior Pull Request for a screenshot

See merge request !295

CHANGELOG

@@ -7,7 +7,7 @@ v 7.8.0
   - Expose description in groups API
   - 
   - 
-  - 
+  - Add diff syntax highlighting in email-on-push service notifications (Hannes Rosenögger)
   - 
   - 
   - 

app/helpers/emails_helper.rb

@@ -29,4 +29,14 @@ module EmailsHelper
       end
     end
   end
+
+  def add_email_highlight_css
+    Rugments::Themes::Github.render(:scope => '.highlight')
+  end
+
+  def color_email_diff(diffcontent)
+    formatter = Rugments::Formatters::HTML.new(cssclass: 'highlight')
+    lexer = Rugments::Lexers::Diff.new
+    raw formatter.format(lexer.lex(diffcontent))
+  end
 end

app/views/layouts/notify.html.haml

@@ -16,7 +16,7 @@
       font-size:small;
       color:#777
     }
-
+    #{add_email_highlight_css}
   %body
     %div.content
       = yield

app/views/notify/repository_push_email.html.haml

@@ -23,7 +23,7 @@
         = diff.new_path || diff.old_path
     %hr
     %pre
-      = diff.diff
+      = color_email_diff(diff.diff)
     %br
 
 - if @compare.timeout