WEB: Adding new pandas logo
- [X] closes #21376, xref #28521
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

![logo_screenshot](https://user-images.githubusercontent.com/10058240/66708951-9ae55280-ed1f-11e9-9621-b482a3af345c.png)

