Properly handle the case where QtWidgets is not available.

It does use a config test for now, just to make it clearer.  The Mac
backend currently requires widgets, but most of the others should work
without it (just not supporting QVideoWidget/WindowControl).

The QVideoDeviceControl interface was modified to remove the QIcon
usage - it was never implemented.

Unfortunately even the QML examples need widgets for the wrapper
application, and will need to be ported to QtGui based wrapper.

Change-Id: I8a55ad5cf09ab51749510bf16f49de0bd3f0bcdb
Reviewed-by: Ling Hu <ling.hu@nokia.com>

src/src.pro

@@ -1,19 +1,30 @@
 TEMPLATE = subdirs
-CONFIG += ordered
-
-library_qgsttools.subdir = $$IN_PWD/gsttools
-library_qgsttools.depends = multimedia
-
-library_qtmmwidgets.subdir = $$IN_PWD/multimediawidgets
-library_qtmmwidgets.depends = multimedia
 
 SUBDIRS += multimedia
 
-contains(config_test_gstreamer, yes) {
-    SUBDIRS += library_qgsttools
+# Everything else depends on multimedia
+src_qgsttools.subdir = $$IN_PWD/gsttools
+src_qgsttools.depends = multimedia
+
+src_qtmmwidgets.subdir = $$IN_PWD/multimediawidgets
+src_qtmmwidgets.depends = multimedia
+
+src_plugins.subdir = $$IN_PWD/plugins
+src_plugins.depends = multimedia
+
+src_imports.subdir = $$IN_PWD/imports
+src_imports.depends = multimedia
+
+SUBDIRS += src_imports
+
+# Optional bits
+contains(config_test_gstreamer, yes):SUBDIRS += src_qgsttools
+contains(config_test_widgets, yes) {
+    SUBDIRS += src_qtmmwidgets
+
+    # If widgets is around, plugins depends on widgets too (imports does not)
+    src_plugins.depends += src_qtmmwidgets
 }
 
-SUBDIRS += library_qtmmwidgets
-SUBDIRS += imports
-SUBDIRS += plugins
+SUBDIRS += src_plugins