E-Mail notifications: include name/link of channel/room

[rasos]

Your Rocket.Chat version: 0.34
In E-Mail notifications, provide a link to the room, where the notification has been triggered.
Currently, only the message content itself is being sent.
Possibly offer an option, that not a link, but only the channel/room name is included, in order to prevent users to open a new browser window, if they have RC already open in a browser or App.

This is related to #741 , which seems to be mostly done, to #1602 to enable E-Mail notifications always and to a digest option for E-Mail notifications.