Added `openssl_verify_mode` parameter for action_mailer.

- parameter in `environments/production.rb`
- documentation & default value (nil) in `discourse_defaults.conf`
Update discovery_topics_view.js

I guess this is a typo
fix funky French language on 503 error page.
BUGFIX: 404 on /users/:user/private-messages
BUGFIX: do not lightbox oneboxed images
Merge pull request #2332 from rhacker/patch-1

Update discovery_topics_view.js
Merge pull request #2334 from pierremanceaux/master

fix funky French language on 503 error page.
BUGFIX: could not see the revisions of a post in a deleted topic
In web crawler mode, don't show a previous link on a page with 0 results. Google will index those pages and keep following the prev links.
TRIVIAL: slightly better information when logging download error
ES6: Notification controllers, added helper to create via ES6/container
Add require to jshint
FIX: moderators can't see private topics that they aren't invited to see.
Plugin Backwards compatibility layer for ES6
FIX: Allow users to create protocol relative URLs in posts.
Add a way to show a custom message at the top of all notification emails. Customize it at /admin/site_contents/notification_email_top
update logster
remove subcategories text from categories page
minor copy improvement
minor mobile fixes