Export the block's line-height settings to html

Task-number: QTBUG-28404

Change-Id: I87e03ecd981c302a5aefdadf7bcfd9729e37bd13
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>