Replacing the figure and script about the GapEncoder in the homepage with something else

[rcap107]

We have been de-prioritizing the GapEncoder a lot, but it's still one of the first things that people see when they open the homepage.

I think we should replace it with something else:

• A simple change would be using the SquashingScaler as the "poster encoder"
• A more complex alternative would be using something like the sphinx card-carousel to have multiple figures, which would allow to potentially have the SquashingScaler, DatetimeEncoder and StringEncoder all in the front page.

My suggestion is to start with the SquashingScaler and then move to the card carousel in a later PR.

[rcap107]

From meeting: the DatetimeEncoder with periodic features is better than the SquashingEncoder. We can also go with the carousel, but later.