Add RTL support to Discourse CSS pre-processing using the RTLit gem and configurable via discourse.conf
ensure rtlit gem in Gemfile is not required by default
ensure RTLit gem is included and CSS is RTLed if css_rtl is enabled in discourse config
Have reciever handle multiple To addresses
Use same reply-to format in all email fixtures
Add error reply for new error
Implement SSO overriding avatars.

Implemented by having Discourse download the image from the provided URL
and treating it as a custom upload.

Adds two more parameters to the SSO site’s response:

* `avatar_url` specifies the URL of the overriding avatar.
* `avatar_force_update` Discourse does not re-download avatars that
has already been download from the same URL. Setting this to true forces
Discourse to re-download the avatar in `avatar_url`

Note that both parameters are ignored if `sso_overrides_avatar` is set
to false.
Fix min_trust_level for wordpress

min_trust_level in the wordpress method was being set to 1 always, the order of the ternary operator was reversed.
UX: Move topic entrance widget to posts column
FIX: Moving posts was not updating `reply_count` and
`reply_to_post_number` so reply linkage was broken.
Upgrade moment.js to latest version, add missing locales now that we
support more languages.
FIX: Broken locale specs
FIX: Using a binding in an `{{avatar}}` was broken
FIX: Float site settings were marked as overridden, reset didn't work.
TRIVIAL: fix deprecations due to momentjs upgrade
remove posts column from /categories
FIX: banner on small desktop screen
remove the "view all {number}.." from mobile cat
missed the posts TH on /categories
FIX: vBulletin wasn't importing posters...