escape gravatar URLs to comply with W3C standards

This fixes an HTML validation error due to & not being properly escaped on the gravatar URLs.
fixes user specs about ampersands in gravatar URLs
TRIVIAL: remove puts statement (cc. @eviltrout)
Add a SiteSetting to configure how many topics are in the email digest.
FIX: Link to user profile broke the back button
BUGFIX: if SSO is enabled invite system is disabled
FEATURE: custom fields on User
Display username and granted at on badge page.
Move badge styles from desktop to common/base.
Merge pull request #2287 from vikhyat/badge-system

Display username and granted_at on badge page
BUGFIX: pull hotlinked images job wasn't properly handling the InvalidParameters exception
BUGIFX: generate avatars when using S3 store
Don't show link counts in the body of posts for internal links. They are
already in the sidebar.
Allow admins to choose if groups are visible or not.
add pluralization rules in ember for Korean (ko)
remove unnecessary css witdh
SECURITY: self XSS by admin by editing badge name
UPGRADE: sidekiq to sidekiq 3.0
FEATURE: alllow unicorn master to fork sidekiqs, keep alive coming
FEATURE: unicorn sidekiq will restart sidekiq on complete failure.

(checks every 30 minutes for complete failure)