centralize and fixup example sources install targets

This follows suit with aeb036e in qtbase.

Change-Id: Ie8580d0a1f38ab9858b0e44c9f99bdc552a1752a
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: hjk <qthjk@ovi.com>

examples/multimediawidgets/multimediawidgets.pro

@@ -0,0 +1,18 @@
+TEMPLATE = subdirs
+
+# These examples all need widgets for now (using creator templates that use widgets)
+!isEmpty(QT.widgets.name) {
+    SUBDIRS += \
+        camera \
+        videographicsitem \
+        videowidget \
+        player \
+        customvideosurface
+
+    QT += widgets
+}
+
+!isEmpty(QT.gui.name):!isEmpty(QT.qml.name) {
+    disabled:SUBDIRS += declarative-camera
+}
+