KCard: Allow the height of sections to be configured and related improvements

[MisRob]

Current behavior

In the first version of KCard, its sections (above title, footer, ...) have fixed height and the card itself has fixed height as well. This is to provide reasonable behavior in regard to consistent sections alignment in a grid row.

Expected behavior

While above still true, KCard needs to be a bit more intelligent to support our many use-cases.

1. Sections' default fixed height can be easily overwritten by consumers
2. To support above, the card's overall height needs to be calculated as a sum total of its sections heights

Ideally, public API to achieve this would be as close as possible to native experience, and would also work with 'auto' height settings that would let sections to take full height of their content (in a grid, this would result in a row being as high as the highest card)

[MisRob]

Related #697