Various cleanups to Ubuntu installation instructions:

* Avoid editing /etc/apt/sources.list add nginx repo, instead create
  /etc/apt/sources.list.d/nginx.list

* Avoid editing /etc/nginx/nginx.conf, instead put server_name_hash_buckets
  setting into discourse.conf

* Proper-case Discourse when it is referring to the product name, so that all
  the lowercase references are to the user created during the installation
Address @Supermathie's concerns in PR1430
Dropping squashing commits from contribution process

 - Rephrases squashing of commits before submitting from a requirement to a recommendation
 - minor fixes around that
Update client.zh_TW.yml

Change for better Traditional Chinese terms 

Admin > 管理員
Moderator > 版主
Posts > 帖子 (sometimes 發表 as a verb )
Topics > 討論話題 (主題 makes user confused with "Themes" ) 
Catogeries > 分類
Mute > 消音 (阻決 is weird )
poster_expansion will only slide down now.
Typo fix

Just another simple typo fix
updated spanish translation

still there are a ton of things to do
Jump to First Post instead of Reloading Topic
add option to override user attributes from SSO payload

add an external_username attribute for username from SSO payload

repair the field name in SingleSignOnRecord migration

move setting of external_username for sso to controller

add settings toggle to override username/email from SSO payload

fix changing of external username after override toggle

complete tests and logic for sso override

add some extra context to username override option

add external_email and external_name to single sign on record

add setting for name override from SSO payload

complete override with stored external_email and external_name

add missing checks to tests

remove an unneeded describe block

break up a monster method for single sign on

fixes for sso attribute override after failed tests
Add plugin specs to travis.
massive update to admin quick start guide
Version bump to v0.9.8.9
add Transifex link to header of translation files
BugFix: email-in on categories wasn't null-ed properly

Causing a problem if two categories got saved with an empty string because the corresponding Database constraint on the index would complain about dublicate values
Merge pull request #2054 from ligthyear/fix-broken-cats

BugFix: email-in on categories wasn't null-ed properly
Merge pull request #2053 from vikhyat/travis-plugins

Add plugin specs to travis
Merge pull request #2049 from nbalonso/spanish-translation

updated spanish translation
Merge pull request #2050 from verg/unify_scroll_to_first_post

Scroll to Top of Topic instead of Reloading
Merge pull request #2047 from jpsullivan/patch-2

Typo fix
Merge pull request #2038 from fantasticfears/poster_expansion

poster_expansion will only slide down now.