Add label to the lockscreen config's "Show media controls" checkbox and make QML imports consistent

Summary: {F7164807}

Test Plan: Open the {nav Appearance} tab of the {nav Screen Locking} KCM

Reviewers: #plasma, #vdg, ngraham

Reviewed By: #vdg, ngraham

Subscribers: ngraham, #vdg, plasma-devel, #plasma

Tags: #plasma

Maniphest Tasks: T10862

Differential Revision: https://phabricator.kde.org/D22940

lookandfeel/contents/lockscreen/config.qml

@@ -1,21 +1,20 @@
-import QtQuick 2.4
-import QtQuick.Controls 2.0
+import QtQuick 2.5
+import QtQuick.Controls 2.5 as QQC2
 import QtQuick.Layouts 1.1
 
-import org.kde.plasma.core 2.0 as Plasmacore
-
 RowLayout {
     property alias cfg_showMediaControls: showMediaControls.checked
 
     spacing: units.largeSpacing / 2
 
-    Label {
+    QQC2.Label {
         Layout.minimumWidth: formAlignment - units.largeSpacing //to match wallpaper config...
         horizontalAlignment: Text.AlignRight
-        text: i18nd("plasma_lookandfeel_org.kde.lookandfeel", "Show media controls:")
+        text: i18nd("plasma_lookandfeel_org.kde.lookandfeel", "Media controls:")
     }
-    CheckBox {
+    QQC2.CheckBox {
         id: showMediaControls
+        text: i18ndc("plasma_lookandfeel_org.kde.lookandfeel", "verb, to show something", "Show")
     }
     Item {
         Layout.fillWidth: true