Considering a Qt 5.6 dependency for plasma-workspace

[Aleix Pol]

Hi,
I'd like to suggest a Qt 5.6 dependency for plasma-workspace master
(and maybe other repositories too).

My personal interest is mostly because of the patch that drops KScreen
dependency in plasmashell [1], but I still think it makes sense on
other areas and it's unlikely that plasma 5.7 is going to ever be run
under Qt 5.5 anyway (in fact, Plasma 5.6 won't be run under Qt 5.5
either on most distributions, interestingly).

Thoughts?
Aleix

[1] https://git.reviewboard.kde.org/r/125451/