Update changelog for 5.2.1

Change-Id: Ie67e598578628663fff9cee7b0f82200f575f2b2
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>
Merge remote-tracking branch 'origin/release' into stable

Change-Id: I7e74e90225c27cb22e51c488a6a0e563359042fe