Rich web embed feature

[kharmabum]

• Install webLinkPreview.other.js on identity
• Feature listens to DID_POST_MESSAGE on userAgent
• Feature inspects message for web link attachments, if found, the feature edits the link attachments on the message to include a title and media preview.

Proposed format:

{
    "text": "hey <&b302addb43d94fb39c6e5831fa83a692|nerds>, check out <+db9168cd9dbf43ba99bbcb54823be88f>",
    "entities": {
        "attachments": {
            "db9168cd9dbf43ba99bbcb54823be88f": {
                "type": "link",
                "url": "http://other.xyz",
                "title": "other.js made this title for your link!",
                "preview": {
                    "type": "image",
                    "url": "https://i.imgur.com/QM8cXiE.jpg"
               }
            }
        },
        "groups": {
            "b302addb43d94fb39c6e5831fa83a692": {
                "identity_ids": [
                    "42ee72a1b1c74355a7622434164372b3",
                    "f5d1fa6df7b14a9f856d267890d7afb1"
                ]
            }
        }
    },
    "channel_id": "fcca853db49345f48d2118382fb0f63c"
}

[kharmabum]

I believe this is blocked by https://github.com/other-xyz/other.js/issues/182