feat: row and cell className generator

[gpedro]

usage:

new Grid({
      columns: ['a', 'b', 'c'],
      data: [
        [1, 2, 3],
        [4, 5, 6],
      ],
      className: {
        tr: (row, header) => {
          console.log('tr', { row, header })
          return 'aaa'
        },
        td: (cell, columnId, row) => {
          console.log('td', { cell, columnId, row })
          return 'aaa'
        },

      }
    }).render(ref.current);

resolves #974

[bravo-kernel]

This would be nice 👍