Add a subscription highlight for a channel!

[jeffboys123]

What should be added?

Instead of a channel having a normal highlight for a new message for when someone subs or gifts a subscription to a channel it can have a purple highlight. This could be a setting that is already turned off for all channels and could be an option under "enable highlights for new messages" and have something like "enable highlights for new subscriptions".

Why should it be added?

This would most likely be used for people who are not tabbed into their own channel when getting offline subs or if you are a moderator for another channel. Sometimes it can get confusing when just seeing a normal highlight under my channel!

[zneix]

Duplicate of #1543, being implemented in #1557.