[Releasing] HEADS UP: Qt 5.6.1 branching ongoing

[Oswald Buddenhagen]

The 5.6.1 branch is now available. Please start using it for changes
targeting the Qt 5.6.1 release. 

We will merge the 5.6 branch to 5.6.1 a last time somewhen next week, so
there should be enough time to finalize ongoing changes in 5.6, and
start using 5.6.1 for new changes.

Changes done on 5.6.1 are forward-merged to 5.6, 5.7, and dev - as usual.
Don't cherry-pick in either direction if at all avoidable - as usual.