Many livechat improvements and fixes

to mis-information.

- Fix integration page on livechat manager
- Add responseTime: time until the first answer by an agent
- Add chatDuration: chat duration until it's closed
- Do not show the "leave" button for livechat rooms
- canAccessRoom method now returns all data from the room object
- Allow livechat managers to manage a livechat session

LingoHub based on develop

Allow livechat managers to manage a livechat session

Manual push by LingoHub User: Gabriel Engel.
Project: Rocket.Chat

Made with  by https://lingohub.com

Require admin role to send emails to users.

fix tableflip emoji

the tableflip emoji does not start with U+00AF(¯), only the shrug
emoji does.

Also removed the macron from the descriptions in the translations.

revert i18n

Add option to accept livechats even if no agents online

Add eslint to travis

Fix slackbridge calling setUserActiveStatus as normal user

* fix video message button always shown while typing

* fix exception when closing videomsg dialog if video wasn't started

* fix typo in code enabling video message feature

New page to see the current livechat queue

New livechat API setTheme