Redesign of the homepage (#759)

* Redesign of the homepage

* Add a max-width for discovery cards

* Evenly space the three about columns

* Use document width instead of window width

* Fix linting errors

* Hero alignment with next section

* Center discovery cards

* Limit width of all sections for better alignment on smaller screens

* Use about page for basic unit test

* Keep the same height for all headers in the three columns

* Reduce debounce time

* Update header height after setting visibility

* Adjust discovery section alignment

* Reduce duplication by creating a mixin

* Switch from PNGs to SVGs

* Rotate and optimize SVGs

* Styling fixes