FEATURE: disposable invite tokens
Merge pull request #2538 from techAPJ/patch-1

FEATURE: disposable invite tokens
FEATURE: Require Javascript to activate an account via email link
FEATURE: add site setting leader_links_no_follow to control whether users with trust level 3 or higher have nofollow on their links
FIX: Work with phpBB import style links with ellipsis
FIX: Combobox wasn't matching selected value properly with value of 0
FEATURE: add site setting allow_new_registrations which can be used to block all new account registrations
FIX: Don't put iframes in emails where they are sanitized out. Replace
them with links.
make Send Test Email easier to see
FEATURE: add site settings rate_limit_new_user_create_topic and rate_limit_new_user_create_post to have different rate limits for topic and post creation for new users
improve test email copy help
FIX: cache avatars in NGINX
FIX: NoMethodError in on extension.upcase when upload's original filename has no extension.