Add "Mark as unread" option to the room list

[wakkorottix]

Description:

#8915 Adds an "Mark as read" option to the room list,
is it possible to add an "Mark as unread" option to the room list? (like in Skype)

Server Setup Information:

• Version of Rocket.Chat Server: 0.59.6
• Operating System: Ubuntu 16.04 LTS 64-bit
• Deployment Method(snap/docker/tar/etc): snap
• Number of Running Instances: 1
• DB Replicaset Oplog:
• Node Version:

Steps to Reproduce:

Expected behavior:

"Mark as unread" at the room list options (like in Skype)

Actual behavior:

Relevant logs: