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
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
Add test to ensure creation of like notification in a PM.
Merge pull request #2056 from vikhyat/pm-likes

Don't suppress like notifications in private messages
FEATURE: Allow `customHTML` helper to resolve to a template if it
exists.
Add Dismiss Read to mobile view
FIX: We should use partials when rendering but keeping the same context.
Update onebox gem to fix stackexchange URL issue