Draw the lock screen video from the OWE lock feed

The shell drops its own player: BackgroundMedia is image-only, and the
lock loads Owe.LockFeedSurface through a Loader, so a system without the
module shows no lock video instead of losing the whole lock screen. The
feed pauses per output when the panel blanks or power saver turns on.

The lock view keeps its still effect path and darkens the feed for
legibility. QtMultimedia and the shell video pause policy are gone, and
the base package list requires owe and owe-lockfeed instead.

shell/plugins/lock/LockFeedSurface.qml

@@ -0,0 +1,11 @@
+import QtQuick
+import Owe.LockFeed
+
+// Loaded through a Loader from LockView, so a system without the module shows
+// no lock video instead of losing the whole lock screen.
+LockFeed {
+  id: root
+
+  property bool feedEnabled: true
+  active: root.feedEnabled
+}