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
Fix Post-rendering bug

Ember.Handlebars.normalizePath was being called with an object as
argument which caused it to error out.
also wrapped the return in a SafeString, so the html will not get
escaped again.
fixing the admin icon in the compose window
Merge pull request #1825 from awesomerobot/master

fixing the admin icon in the compose window
FEATURE: better top pages
BUGFIX: properly hide categories/top lists view when loading another tab
BUGFIX: cannot sort topic
Disallow auth callbacks in robots.txt
Delegate :username rather than using a class method.

This is just a little cleaner?
Page title includes page number for web crawlers
BUGFIX: groups page wasn't working
Fix group matching SQL query

The check there is intended for the :members_mods_and_admins level, which is not automatically checked for normal users. Instead, the :everyone level is the one used, which would always fulfill the "alias_level in :levels" check.

This changes the :everyone level to :members_mods_and_admins, which was originally intended.
Change to case-insensitive matching in group @name matching
BUGFIX: could not save user's preferences when categories where watched/tracked/muted
FIX: Accept HTTPS or HTTP urls on redirect
FIX: Allow click tracking to work with different origins
FIX: Incorrect string match
FIX: When embedded, don't show button at the top unless there are more than 10 posts.
BUGFIX: emoji's url were relatives (was breaking the wordpress plugin)