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
Merge pull request #1837 from shivpkumar/master

sub space for underscore in 'name' when registering public folder in plu...
Update client.zh_CN.yml
Merge pull request #1838 from ofgeek/patch-1

Update client.zh_CN.yml
Update server.zh_TW.yml

modify chinese words/sentences to HK/TW style.
Merge pull request #1840 from worminfo/patch-2

Update server.zh_TW.yml
force_encoding according to the charset in mail, this solve encoding problem when not using ‘utf-8’ charset.
Merge pull request #1835 from HerbJiang/master

Fix reply by email encoding error when using non-ASCII & non-UTF8 charset
BUGFIX: remote upload dialog was broken
REFACTOR: Fixes poor class hierarchy for listing topics

- Upgrades Ember to latest
- Fixes a bunch of bugs with page titles and missing "active" states
Lots of bugfixes

BUGFIX: navigation bar should always activate the right tab (even when diging into a top period)
BUGFIX: /top pages titles
BUGFIX: no "edit category" button on /top page after visiting a category
BUGFIX: properly hide category columns when there is no children category (on both filter + top pages)
BUGFIX: promises not caught when scrolling down a topic list to load more of them
BUGFIX: CSS on category dropdowns
Updated `top_menu` i18n with available filters
fix the specs
BUGFIX: url was overriden when using the back button after visiting a topic
BUGFIX: proper handling of /none subcategory
BUGFIX: display links to other periods at the bottom of the top/:period page
remove duplicated order_with_pinned_sql method
FEATURE: show pinned topics for TL0 on top/year page

BUGFIX: word-wrap on topic-excerpt
changed `topics_per_period_in_top_page` default to 100
Clarify commands around rvm