Show/Hide Python 3 ready packages

[c17r]

Now that the scales have tipped way in favor of Python 3, make it easy to see ones that still need porting.

CSS button rounding moved into code since last-child/first-child pseudo selectors are absolute and not "last/first visible"

Not married to button size and/or location. Changes as necessary.

[chhantyal]

Hi, thanks for your PR.

Could you please attach screenshot?

[c17r]

Sure. Here it is when you first load the page:

And after you click the button:

If you click it again, it goes back to showing everything.

[chhantyal]

Thanks a lot and sorry for delay