Add "This message relates to: *gig/request*" chat notification when a buyer replies to a Buyer Request offer

[svrockwell1]

Context:
- On desktop, a buyer's name is not visible to a seller prior to an offer's submission.
- First-time messages from buyers replying to a seller's BR offer are indistinguishable from conversations initiated through a seller's profile's "Contact Me" button.

Adding a "This message relates to: *gig/request*" notification when a buyer replies to a seller's offer will:
1. Exempt the buyer from having to explicitly reference their original request, allowing them to focus on the details important to their project and move the conversation forward.
2. Save the seller time from rifling through old offers in search of the one they're being contacted about. The benefit from this increases for sellers sending out multiple offers per day/week. The longer the period between sending out an offer and receiving a buyer's reply, the more valuable the notification becomes.
3. Reduce ambiguity and allow both parties to put their best foot forward in an informed, streamlined, and professional manner. 

That's it. That's the rant.