improve lighthouse 'performance' score

Current lighthouse scores are:

| Metric         | Score |
| -------------- | ----- |
| Performance    | 96%   |
| Accessibility  | 100%  |
| Best Practices | 100%  |
| SEO            | 100%  |

Improve lighthouse 'performance' scores by doing the following:
- optimize hero/header image
- reduce unused javascript
- properly size github star image