[Releasing] HEADS UP: Qt 5.7 branching ongoing

[Oswald Buddenhagen]

with some rather significant delay, the 5.7 branch is now available.
please start using it for new changes intented for the Qt 5.7 release. 

we will downmerge dev to 5.7 the last time in a few days - i don't know
any particular date, but it may be *quite* soon, as we're running late.
it's recommended that you send retargeting requests for pending changes
on dev meant for 5.7 to me immediately. if the changes still integrate
on dev before monday, that's fine.