add At.js and dependencies

apps/comments/js/vendor/At.js/examples/style.css

apps/comments/js/vendor/At.js/examples/tinyMCE.html

apps/comments/js/vendor/At.js/examples/ueditor.html

apps/comments/js/vendor/At.js/gulpfile.js

apps/comments/js/vendor/At.js/index.html

apps/comments/js/vendor/At.js/package.json

apps/comments/js/vendor/At.js/specRunner.html

apps/comments/js/vendor/At.js/src/api.coffee

apps/comments/js/vendor/At.js/src/app.coffee

apps/comments/js/vendor/At.js/src/controller.coffee

apps/comments/js/vendor/At.js/src/default.coffee

apps/comments/js/vendor/At.js/src/editableController.coffee

apps/comments/js/vendor/At.js/src/jquery.atwho.css

apps/comments/js/vendor/At.js/src/model.coffee

apps/comments/js/vendor/At.js/src/textareaController.coffee

apps/comments/js/vendor/At.js/src/view.coffee

apps/comments/js/vendor/At.js/umd.template.js

apps/comments/js/vendor/Caret.js/.bower.json

apps/comments/js/vendor/Caret.js/CHANGELOG.md

apps/comments/js/vendor/Caret.js/Gruntfile.coffee