chore(table): cleanup docs and builder methods (#638)

- Refactor the `table` module for better top to bottom readability by
putting types first and arranging them in a logical order (Table, Row,
Cell, other).

- Adds new methods for:
  - `Table::rows`
  - `Row::cells`
  - `Cell::new`
  - `Cell::content`
  - `TableState::new`
  - `TableState::selected_mut`

- Makes `HighlightSpacing::should_add` pub(crate) since it's an internal
  detail.

- Adds tests for all the new methods and simple property tests for all
  the other setter methods.