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
Add Global Keyboard Shortcuts

Not all of these have been fully implemented yet.

**Jump To**
* `g` then `h` - Home (Latest)
* `g` then `l` - Latest
* `g` then `n` - New
* `g` then `u` - Unread
* `g` then `f` - Favorited
* `g` then `c` - Categories List

**Navigation**
* `u` - Back to topic list
* `k` / `j` - Newer/Older conversation or post
* `o` or `Enter` - Open selected conversation
* <code>`</code> - Go to next section
* `~` - Go to previous section

**Application**
* `c` - Create a new topic
* `n` - Open notifications menu
* `/` - Search
* `?` - Open keyboard shortcut help

**Actions**
* `f` - Favorite topic
* `s` - Share topic
* `<Shift>` + `s` - Share selected post
* `r` - Reply to topic
* `<Shift>` + `r` - Reply to selected post
* `l` - Like selected post
* `!` - Flag selected post
* `b` - Bookmark selected post
* `e` - Edit selected post
* `d` - Delete selected post
* `m` then `m` - Mark topic as muted
* `m` then `r` - Mark topic as regular
* `m` then `t` - Mark topic as tracking
* `m` then `w` - Mark topic as watching
Add a few extra ProxyPass calls

These avoid a lot of 404 errors, and things like the style editor not working because the browser can't reach scripts, etc.
clean up images max-width mess in the CSS
FEATURE: allow for custom HTML inside the <head> tags
In development mode, relax restrictions on embedding.
BUGFIX: export rake task should include locally stored avatars
FIX: Missing variable
Link embeded topic to second post. They've already read the first.
FIX: Broken test
Don't employ the "too many replies" if the user is staff, or if they created the topic.

See: http://meta.discourse.org/t/what-is-the-point-of-limiting-new-users-to-three-replies-per-topic/11696
FIX: Support feeds with `description` as well as `content`
Add default_external_links_in_new_tab site setting
FEATURE: improve the TOP page scoring formula a bit
Minor update to ember-renderspeed
FIX: Logo needs target=_blank