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
minor digest email copyedits
improve test email error message
BUGFIX: add h2 with period when browsing top pages
BUGFIX: only redirect users top /top page once
clarify register account
better first boot register admin account help
Update INSTALL-digital-ocean.md
incorrect image urls in guide
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