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.
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.
Merge pull request #2046 from staryume/patch-4

Update client.zh_TW.yml for better Tradtional Chinese translations
Merge pull request #2033 from birarda/master

add option to override user attributes from SSO payload