support/scripts/pkg-stats: fixed sortGrid() performance

sortGrid() has been rewritten to dynamically generate stylesheets with
explicit grid-row properties to re-order the rows, instead of removing
and reinserting the cells.
Performance *should* now be comperable to sorttable.js.

Signed-off-by: Sen Hastings <sen@phobosdpl.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>