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
changed `topics_per_period_in_top_page` default to 100
Clarify commands around rvm
BUGFIX: move mobile templates to discovery
BUGFIX: edit category button should only be shown to staff members
Update client.zh_CN.yml
Merge pull request #1842 from ofgeek/patch-1

Update client.zh_CN.yml
Update server.nl.yml
Update client.nl.yml
Typo in scripts/discourse
Simplify example, remove typo
BUGFIX: clicking cancel should not reload the page

when assets have changed.
Merge pull request #1845 from sanderdatema/patch-3

Typo in scripts/discourse
Merge pull request #1844 from sanderdatema/patch-1

Dutch language updated
BUGFIX: properly escape HTML entities in excerpt (props to @ecuk)
UI: missing space
BUGFIX: missing styling
FEATURE: collapse PM notifications
BUGFIX: computed.alias (and even property) seems bust in components