Merge pull request #2374 from RocketChat/pinned-message-notification

...ges/rocketchat-importer-slack/server/SlackImporter.coffee

packages/rocketchat-lib/server/models/Messages.coffee

...ages/rocketchat-livechat/app/client/stylesheets/main.less

packages/rocketchat-message-pin/client/messageType.js

packages/rocketchat-message-pin/i18n/en.i18n.json

packages/rocketchat-message-pin/package.js

packages/rocketchat-message-pin/server/pinMessage.coffee

packages/rocketchat-theme/assets/stylesheets/base.less

...etchat-theme/assets/stylesheets/utils/_colors.import.less

packages/rocketchat-ui-message/message/message.coffee

packages/rocketchat-ui/lib/avatar.coffee

packages/rocketchat-ui/lib/getAvatarUrlFromUsername.coffee

packages/rocketchat-ui/package.js