Rocket.chat: Ability to link to individual messages

[dandv]

Use case: send someone a link to a specific part of the conversation in a given channel

This can almost be done right now via search (see #946), but the URL should be updated with a permalink to the message, probably based on its _id.

Another enhancement would be to have a "link" context menu item next to Star and Reactions:

[andreas-bulling]

+1

[royalaid]

Just context Slack implements this by a link that can be copied by right-clicking the timestamp of a message