feature: use select2 instead of chosen
quoting fixes

- allow bbcode quotes to be nested
- don't allow the '=' to be omitted from quotes
- fix some css that made assumptions about nested quotes
Merge pull request #2333 from rhacker/select2

feature: use select2 instead of chosen
Support images from the select2 plugin
Minor CSS fixes for Select2
Merge pull request #2382 from BenLubar/patch-quotes

quoting fixes
FIX: Sass helper mismatch
Also warn admins when there aren't at least 50 posts
FIX: typo in vendor/gems/discourse_imgur/lib/discourse_imgur/locale/server.zh_CN.yml
ES6: Migrate a few components over
add note about root password change prompt
BUGFIX `-` in domain name not captured by route
we lost my "public" copy change
update Admin Quick Start guide a bit
Update uglifier to latest
HACK: work around https://github.com/mishoo/UglifyJS2/issues/328