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
Dropping squashing commits from contribution process

 - Rephrases squashing of commits before submitting from a requirement to a recommendation
 - minor fixes around that
FEATURE: only redirect new users to top page for a limited period

That period is defined by the `redirect_new_users_to_top_page_duration`
site setting and defaults to 7 days.
BUGFIX: Editing a category would break categories for the current user
session.
adding basic :focus style in for buttons in Firefox
Merge pull request #2057 from awesomerobot/master

adding basic :focus style in for buttons in Firefox
modifying user profile to better support image backgrounds
Merge pull request #2058 from awesomerobot/master

modifying user profile to better support image backgrounds
Remove empty SCSS rules
Merge pull request #2059 from nschonni/remove-empty-rules

Remove empty SCSS rules
Remove units for zero values

Units are ignored for zero values in CSS except for a few edge cases.
Merge pull request #2060 from nschonni/remove-units-for-zero-values

Remove units for zero values
Use for loop to shrink bbcode

Dry out the long set of similar selectors
Strip tabs from sheets
fix translate mistake

Line 626
minor change : favourite > starred
Merge pull request #2063 from CirnoKaster/patch-1

fix translate mistake
Merge pull request #2061 from nschonni/use-loops-for-bbcode

Use for loop to shrink bbcode
Update client.zh_TW.yml

Minor fixes for the chinese translations
BUGFIX: topic specs were dependent on Time.now

which would fail when DST was around