Add "Why this domain?" to hard-coded site list for non-obvious Facebook URLs

[maxxcrawford]

Summary:
Add a panel notification for why a certain domain is inside the Facebook Container.

Reasoning:
If we are to add more hardcoded domains to Facebook, as the domains get more and more seemingly unrelated to Facebook, we should explain it. It would better inform the users of how vast Facebook's footprint is.

Copy (Rough draft)

• Headline: [Domain] domain is owned by Facebook
• Text link: Learn more about this website's relationship here. (Link to article/etc about being owned by Facebook)

Example:
User goes to https://mapwith.ai site and is opened in the FB Container

Related issues:

• Broken facebook site: https://mapwith.ai #551
• Expand Facebook-owned domains into default URL list #558
• CFR Recommends FBC on WhatsApp website but WhatsApp is not included in default domain list.  #652
• Feature request: Include fb.me #108
• Add Giphy to Facebook container #643

Open PRs that cover additional domains:

• Fixed #467 - Added additional FB owned domains to the default list #472
• Facebook Domain Overhaul (many, many added) #499
• Add instagram-press.com to Instagram domains #524