Refactor the next actions screen and the .card CSS class

[felipealencar]

The current next actions screen is using margin-bottom and position: absolute properties to position elements (cf. .card class) . As the .card class is used in other places, it sometimes may break the HTML elements' flow.
A better option would be designing the next actions screen using a Grid layout.

[kate-holdener]

Thanks @felipealencar . This is somewhat connected to issue #3 : the current next actions screen shows way too many possible actions, which is confusing for someone not familiar with building ML pipelines. However, I think the refactoring of the screen can happen independently of work on issue #3, since refactoring would all be on the front end.