This commit provides a heavy proofreading of zh-CN translations, and
mainly draws from the zh-HK source when a translation is found too
incoherent. Translating directly from en is used when zh-HK translation
is not available.

This commit also completes the tweet-toot (choo-choo, actually) for
zh-cn introduced in #2044. Some minor copyediting, as well as
additional en translations, has been fed back into zh-hk text.

* Add missing fields group on preferences page

* Clean up settings/preferences controller

* Extract a UserSettingsDecorator

* Repair most egregious mistakes

The deployed changes broke the pedagogy and curriculum built into the design of the onboarding modals, which had been reviewed and approved by various other contributors. While the changed layouts of the pages make some of the original decisions impossible to re-implement without substantial work, these changes should at least make the modals not outright terrible. 

The empty confusing description of Mastodon was replaced with an actual basic explanation of federation. The language was modified to be friendly and conversational again. Grammatical errors were fixed. The explanations of local and federated timelines were re-ordered to be in the direct that the menus go, top to bottom, and the sentence was re-added which explains that they are what "public timelines" refers to (since this phrasing is used elsewhere in the UI) and suggests the user use them to discover who to follow. A figure of the profile picture that lives above the compose box was padded to page two to serve as a landmark for less technically literate users to easily find the compose box and understand that the next page is moving upwards, so that they can find the search bar. 

Ideally, the elephant artwork should be either removed or replaced with something less depressing.  Room should be made to point users at the notifications column's settings icon because "how do I turn off the notification noise" is one of the most asked questions of new users and those icons are not easily noticeable. This last part may be made obsolete if the settings UI is later re-worked.

* Change copy

This commit addresses copy change suggestions made in the PR discussion

* Add periods to ends of sentences missing periods
* Made "Home" "Federated" "Local" and "Notifications" lowercase
* Separate explanation of "connecting" and the word "instance" into two sentences, to make the sentence less dense.

* Alphabetically order translation keys

* Fix some missing gender neutral translations in french

* Add a comment to remind contributors to order translations by key

* Add render_views for admin/settings spec

* Add coverage for admin/settings#update

* Add coverage for admin/settings typecasting open_registrations setting

* Simplify how admin/settings finds the value for updating

* Rely on activerecord to not update a value that hasnt changed

* Add coverage for non-existent setting

* Use a constant for boolean settings

* after yarn upgrade

* after manually removing node-gyp as top level dependency

* Fix #2120 - Use Status#as_tag_timeline on public hashtag page

* Update tags_controller.rb

Send nil for SMTP_LOGIN or SMTP_PASSWORD if it was left blank in the envfile, otherwise Ruby still attempts auth even if SMTP_AUTH_METHOD is none (#2180)

* Fix #2108 - Fix gif uploads
Add specs for media attachment gifv conversion

* Add ffmpeg to travis

* Make travis install ffmpeg, not libav

* Switch travis to trusty

* Fix possibility of unrightful webfinger redirect

* Add more tests for FollowRemoteAccountService

* Add meta tags for OGP to following & follow page

* simplify render helper

* Follow up #2133

* og:type is only accounts/show

* revert accounts/{following,followers}

add 'result' mean, '件' only mean count unit.

* Added it.jsx

* Update index.jsx

* Update mastodon.jsx

* For undownloaded attachments, set type :unknown, display them as a list in the web UI

* Fix case when attachment type is set explicitly

* fix character escaping in URL

* add tests

* put a comma after the last item

* add HTML escape test

* enable to scroll the setting's page sidebar

add scroll:auto and use margin instead of padding for the bottom

* Update admin.scss

* Update admin.scss

* Update admin.scss

Previously the `bin/setup` script only installed the Ruby dependencies
via Bundler. This is not sufficient to get the test suite to pass. We
also need the JavaScript dependencies.

This commit installs the JavaScript dependencies as part of the
`bin/setup` script via Yarn.

This allows for a successful

    bin/setup && bundle exec rake

on a fresh clone of the repo.

Related to #1533.

* Do not show link preview card if toot has a spoiler

* == to ===