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
cleans up site map integration tests
FIX: Broken unsubscribe link in HTML email
Performance: reduce max length post model for testing purpose
added KBD style back
The Rails JSON encoder API requires `as_json` to take an optional arg
Don't abuse as_json, it's not meant for consumption

The `as_json` API is a hook for JSON encoders to call, not meant for
consumption like this, and the result is not guarenteed to be stable
across Rails versions.

There might be other cases like this that we should revisit later, but
this one in particular is causing a test to fail on Rails master.
Merge pull request #1706 from awesomerobot/master

added KBD style back
Merge pull request #1708 from chancancode/dont_abuse_as_json

Don't abuse as_json, it's not meant for consumption
Merge pull request #1707 from chancancode/as_json_fix

The Rails JSON encoder API requires `as_json` to take an optional arg
Fix email_preview AJAX call to use Discourse.ajax
cors for fonts, so firefox stays happy
break cache of fonts
message bus and vestal versions update
auto close is messed up in category edit, remove for now
skip validations for Spam Rules when needed