Support single redis DB.
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
Locate the Puma config file.
Update puma.rb
Russian translation (actual version)
Admin Quick Start Guide: Change email test link

The feature has moved from `/admin/email/logs` to `/admin/email`.
Merge pull request #1742 from joallard/patch-1

[minor] Admin Quick Start Guide: Change email test link
Improve how category stats are rendered
Improve tooltip on categories stats.
FIX: Title text should be correctly escaped since we are generating a raw html.
IMPORTANT - removed all sample files
This is very likely to cause merge conflict, it is for the greater good
Discuss at: http://meta.discourse.org/t/enough-with-the-sample-files/10351

From now on we use ENV to customise if needed
default to a db called postgres
fix error message
correct parsing
attempt to bypass setting port if socket is provided
fix travis
attempt to make travis less upset
improve config so you can use it with a socket optionally
Update client.zh_CN.yml