Add support for ENS name avatars

Nobody has claimed this yet.

**Describe the usability problem**
ENS allows a user to add an avatar to their ENS name, via the avatar text record. (see example [here](https://app.ens.domains/name/brantly.art)). MetaMask already uses reverse resolution to show my ENS name on my homepage in the app, as well as in the Send From field, which is great. But right now it shows the blocky image generated from that address. Would be great to show the image in the name's avatar text record (if it exists), and only fall back on the blocky image if there is no image in the name's avatar text record.

You could also show a name's avatar in the Recipient field as well after I type it in.

**Screenshots**
_If applicable, add screenshots or links to help explain the issue_

**Expected behavior**
Any where that an ENS name is displayed, whether from reverse resolution or a users typing it, check to see if the name has an image in the avatar text record. If so, display it. If not, fall back on the blocky image.

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**User impact | Usage frequency | Feasibility scores**
Makes the app and a person's wallet and ENS experience much more user-friendly and visually friendly.

The issue identifies ENS reverse resolution, the avatar text record, the Send From field, and the Recipient field; start by tracing those name-display flows in the mobile app. Done means ENS avatars appear wherever ENS names are shown, with the blocky image used only when no avatar text record image exists.

Written by the indexing model from the issue text.