Forward open livechat rooms from agent when he goes offline

packages/rocketchat-lib/i18n/en.i18n.json

packages/rocketchat-livechat/app/client/views/message.coffee

packages/rocketchat-livechat/app/i18n/en.i18n.json

packages/rocketchat-livechat/config.js

packages/rocketchat-livechat/package.js

...es/rocketchat-livechat/server/forwardUnclosedLivechats.js

packages/rocketchat-livechat/server/lib/Livechat.js

packages/rocketchat-livechat/server/models/Rooms.js