Add changelog for 5.3.1

Change-Id: I5d9c67a2f89c0c191de9e6de24d068fca17dba0e
Reviewed-by: Jani Heikkinen <jani.heikkinen@digia.com>
Merge remote-tracking branch 'origin/5.3.1' into 5.3

Change-Id: Ic4418ade05ff7d89cbb375a25d9fd80353a2317a
Merge "Merge remote-tracking branch 'origin/5.3.1' into 5.3" into refs/staging/5.3