Add smart row wrapping and cleanup table drawing

[joaemel]

This PR contains two features improving the handling of null/not drawn borders I needed since I use boxable for layout.

It makes page wrapping a bit smarter. This prevents page breaks at visually wrong locations with null borders.
The rows that are allowed to be wrapped to the next page can be customized using an interface similar to the one for word wrapping.

Additionally, I cleaned up the logic for top border removal, and made it only remove the next top border, if the previous bottom border exists. This e.g. allows you to use borderless rows as separator between tables, without making those tables lose their top borders.
This is very basic and could be improved further, allowing conflicting border styles and partial borders to be handled better.