KF 5.37 requiring Qt 5.7

[David Faure]

According to the policy that KF5 should work with the last 3 releases of 
Qt5.x, it is time now for upcoming releases of KF5 to drop support for Qt 5.6.

Packagers: is that acceptable?

Normally I would have just gone ahead with applying the policy, but after my 
recent finding that even some very recent distributions are still on Qt 5.6 
LTS, I just want to make sure.

(On the other hand I guess it's fine in the actual case I know about, given 
that the OpenSuSE KDE:Frameworks5 repo is based on Qt 5.9)

-- 
David Faure, faure at kde.org, http://www.davidfaure.fr
Working on KDE Frameworks 5