#791 Use ESCET logo in relevant places on the website

• Best to review per commit.
• Uses the new logo on the website:
  • On the home page.
  • As favicon on static pages.
  • As favicon on documentation pages.
  • In the icon selector dropdown menu.
• I've also add the icon in various resolutions. I used them for the website, but we'll also need them for the IDE in a next merge request for this issue.

Addresses #791 (closed)