Cannot /invite users to a livechat

[sampaiodiego]

Description:

If you /invite someone to a livechat session, if that person is not a livechat agent or livechat manager, it will not see anything. But it he is, it will see a link to the room but will be able to open it.

Server Setup Information:

• Version of Rocket.Chat Server: 0.61.2
• Operating System: Any
• Deployment Method(snap/docker/tar/etc): Any
• Number of Running Instances: 1
• DB Replicaset Oplog: Yes
• Node Version: 8.9.4

Steps to Reproduce:

1. Have a livechat
2. /invite someone (yes, using the slash command)
3. See the person you invite arguing

Expected behavior:

The person invited should be able to open and send messages to the invite livechat.

Actual behavior:

Depending on invited person's role he will not be able to join or don't even see the link to join:

This happens because livechat rooms have an additional field used to compose the room link (the code property on room object), but if you /invite someone, since the /invite command does not know how livechat works, it will not use that information to create the link. So the fix would be stop using the code property on links, and start using the _id, so anything will break.

Additionally, the livechat visitor should not be warned if someone is invited.