Qt version dependency in workspace/

[Eike Hein]

Hi,

after discussion in #plasma today and in light of kwin moving to
a Qt 5.4.0 dependency, we've decided to bump workspace to 5.4.0
as a whole to reduce the support surface and avoid problems
creeping in in the wild.

I've bumped the following repositories today:

bluedevil
kde-cli-tools
kdecoration
kdeplasma-addons
kfilemetadata
khelpcenter
khotkeys
kinfocenter
kio-extras
kmenuedit
ksysguard
kwayland
kwrited
plasma-desktop
plasma-nm
plasma-workspace
polkit-kde-agent-1
powerdevil
sddm-kcm
systemsettings


This leaves a whole bunch of repositories under workspace/
that either don't specify a minimum Qt version yet or I wasn't
sure about them because they're libraries:

baloo
breeze
kcm-touchpad
kde-gtk-config
kscreen
ksshaskpass
libbluedevil
libksysguard
libmm-qt
milou
muon
oxygen
oxygen-fonts
user-manager

oxyen-fonts aside, do we want to add minimum Qt versions to
these? Any objections?


Cheers,
Eike