minor copyedits on new account page
get rid of some needless (?) img styles on mobile
BUGFIX: properly enforce image dimensions on mobile
Merge pull request #2460 from riking/site-settings

Add regex validations for OAuth, UA, and S3 fields
Merge pull request #2461 from peternlewis/pop3s_polling_period_mins

Add a SiteSetting to control the pop3 polling period.
FIX: make pm notification badge green on mobile
Add a note to pop3s_polling_period_mins saying that it requires restart
FEATURE: rake task to clean up all the avatar thumbnails
TRIVIAL: remove commented file
changing the tracking dropdown highlight for consistency
BUGFIX: can't ctrl+click post datestamps
Merge pull request #2463 from awesomerobot/master

changing the tracking dropdown highlight for consistency
FIX: If there is no `last_posted_at` don't raise an exception
FIX: Don't raise an exception when `last_posted_at` is nil
BUGFIX: buttons have a different size when clicked on FF (cc @awesomerobot)

cf. https://meta.discourse.org/t/browse-buttons-in-the-edit-history-have-a-different-size-when-clicked/16698
TRIVIAL: Remove border thickness from handlebars template. Just do the
color there.
ES6: Convert all button views
`[code]` should work just like other kinda of code formatting.
FIX: Load order for non-ES6
FIX: `<pre>` blocks were adding too many new lines.