Add dependencies via Composer

[al-esc]

Related issues: #43 & #44
Dependencies (non-exhaustive):

• https://github.com/harvesthq/chosen
• https://github.com/crowdfavorite/jquery.hotkeys
• https://github.com/crowdfavorite/linkify
• https://github.com/crowdfavorite/sidr
• https://github.com/crowdfavorite/jquery-scrollintoview
• https://github.com/crowdfavorite/JSON-js
• https://github.com/crowdfavorite/twitter-text-js
• https://github.com/crowdfavorite/php-markdown-extra-extended
• https://github.com/crowdfavorite/phpjs
• https://github.com/ajaxorg/ace
  CF-built dependencies:
• https://github.com/crowdfavorite/wp-taxonomy-filter
• https://github.com/crowdfavorite/wp-gatekeeper