Projects page: add fallback avatar image

This should have some placeholder profile picture. Here's the associated event:
{
  "id": "30896298962",
  "type": "ReleaseEvent",
  "actor": {
    "id": 41898282,
    "login": "github-actions[bot]",
    "display_login": "github-actions",
    "gravatar_id": "",
    "url": "https://api.github.com/users/github-actions[bot]",
    "avatar_url": "https://avatars.githubusercontent.com/u/41898282?"
  },
  "repo": {
    "id": 519832,
    "name": "mitmproxy/mitmproxy",
    "url": "https://api.github.com/repos/mitmproxy/mitmproxy"
  },
  "payload": {
    "action": "published",
    "release": {
      "url": "https://api.github.com/repos/mitmproxy/mitmproxy/releases/115087111",
      "assets_url": "https://api.github.com/repos/mitmproxy/mitmproxy/releases/115087111/assets",
      "upload_url": "https://uploads.github.com/repos/mitmproxy/mitmproxy/releases/115087111/assets{?name,label}",
      "html_url": "https://github.com/mitmproxy/mitmproxy/releases/tag/10.0.0",
      "id": 115087111,
      "author": {
        "login": "github-actions[bot]",
        "id": 41898282,
        "node_id": "MDM6Qm90NDE4OTgyODI=",
        "avatar_url": "https://avatars.githubusercontent.com/in/15368?v=4",
        "gravatar_id": "",
        "url": "https://api.github.com/users/github-actions%5Bbot%5D",
        "html_url": "https://github.com/apps/github-actions",
        "followers_url": "https://api.github.com/users/github-actions%5Bbot%5D/followers",
        "following_url": "https://api.github.com/users/github-actions%5Bbot%5D/following{/other_user}",
        "gists_url": "https://api.github.com/users/github-actions%5Bbot%5D/gists{/gist_id}",
        "starred_url": "https://api.github.com/users/github-actions%5Bbot%5D/starred{/owner}{/repo}",
        "subscriptions_url": "https://api.github.com/users/github-actions%5Bbot%5D/subscriptions",
        "organizations_url": "https://api.github.com/users/github-actions%5Bbot%5D/orgs",
        "repos_url": "https://api.github.com/users/github-actions%5Bbot%5D/repos",
        "events_url": "https://api.github.com/users/github-actions%5Bbot%5D/events{/privacy}",
        "received_events_url": "https://api.github.com/users/github-actions%5Bbot%5D/received_events",
        "type": "Bot",
        "site_admin": false
      },
      "node_id": "RE_kwDOAAfumM4G3BcH",
      "tag_name": "10.0.0",
      "target_commitish": "main",
      "name": "mitmproxy 10.0.0",
      "draft": false,
      "prerelease": false,
      "created_at": "2023-08-04T09:37:11Z",
      "published_at": "2023-08-04T09:37:12Z",
      "assets": [],
      "tarball_url": "https://api.github.com/repos/mitmproxy/mitmproxy/tarball/10.0.0",
      "zipball_url": "https://api.github.com/repos/mitmproxy/mitmproxy/zipball/10.0.0",
      "body": "Changes: See [CHANGELOG.md](https://github.com/mitmproxy/mitmproxy/blob/main/CHANGELOG.md).\n\nYou can find the latest release packages at https://mitmproxy.org/downloads/.\n",
      "short_description_html": "<p>Changes: See <a href=\"https://github.com/mitmproxy/mitmproxy/blob/main/CHANGELOG.md\">CHANGELOG.md</a>.</p>\n<p>You can find the latest release packages at <a href=\"https://mitmproxy.org/downloads/\" rel=\"nofollow\">https://mitmproxy.org/downloads/</a>.</p>",
      "is_short_description_html_truncated": false
    }
  },
  "public": true,
  "created_at": "2023-08-04T09:37:13Z",
  "org": {
    "id": 4652787,
    "login": "mitmproxy",
    "gravatar_id": "",
    "url": "https://api.github.com/orgs/mitmproxy",
    "avatar_url": "https://avatars.githubusercontent.com/u/4652787?"
  }
}
honeynet / honeynet.org

Projects page: add fallback avatar image #44
