Add Traditional Chinese, Hong Kong translation (zh-HK) (#1544)

* Added Chinese Traditional Hong Kong (zh-HK) for Ruby

* Added translations for Ruby.

* Added Chinese Traditional Hong Kong (zh-HK) for JS

* Added translations for javascript code.

* Rearrange language references in mastodon.jsx

* Break `addLocaleData` into multiple lines. Make future commit more readable.
* Roughly re-sort the languages in alphabetical orders
  (only manually put English on top because it is default).

* Sort application.rb locale with alphabetical order

With exception that English (default language) goes first.
Improve code readability.

* Resort language selection box alphabetically

Sort HUMAN_LOCALES in the alphabetical order of display name
(except English, the default language, come first).

Improve usability.

config/application.rb

@@ -25,7 +25,21 @@ module Mastodon
     # The default locale is :en and all translations from config/locales/*.rb,yml are auto loaded.
     # config.i18n.load_path += Dir[Rails.root.join('my', 'locales', '*.{rb,yml}').to_s]
 
-    config.i18n.available_locales = [:en, :de, :es, :pt, :fr, :hu, :uk, 'zh-CN', :fi, :eo, :ru, :ja]
+    config.i18n.available_locales = [
+      :en,
+      :de,
+      :eo,
+      :es,
+      :fi,
+      :fr,
+      :hu,
+      :ja,
+      :pt,
+      :ru,
+      :uk,
+      'zh-CN',
+      :'zh-HK',
+    ]
 
     config.i18n.default_locale    = :en