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.
Allow configuration of Redis DB and cache DB

Hardcoding the Redis DB and Redis Caching DB to 0 and 2 in
`config/database.yml` makes an unsafe assumption that Discourse is the
only application using that install of redis-server. Instead of forcing
users to undergo yet another form of configuration, allow Discourse
admins a nicer way to configure the Redis databases used.

Signed-off-by: David Celis <me@davidcel.is>
Merge pull request #1778 from davidcelis/configure-redis-db

Allow configuration of Redis DB and cache DB
Added a rails_master section to Gemfile
No more `with_default_scope` on Rails master, see https://github.com/rails/rails/commit/94924dc32baf78f13e289172534c2e71c9c8cade
Added a reload to fix a test broken on master

I am not sure why this is wokring on Rails 4, but the problem is that `post3`
here is holding on to an old reference of some associations so `PostDestroyer`
is not doing the right thing.
FEATURE: add support for gem source in plugins
Merge pull request #1709 from chancancode/boot_to_master

Make Discourse work on Rails master (4.1)
no need to remove what is not there
FEATURE: allow plugins to overwrite handlebars templates
Merge pull request #1779 from discourse/override-templates

FEATURE: allow plugins to overwrite handlebars templates
Prevent deleting 'uncategorized' category
Support for Embeddable Comments via IFRAME
Use the standard .jshintrc file for JSHint options.