0029571: Samples: build qt samples together with OCCT

Extending CMake procedure by 'BUILD_MODULE_QtSamples' variable to switch on qt samples build.
Implementation required:
- union of occt_toolkit_tool.cmake and occt_toolkit.cmake files;
- correction of qt samples sources by adding path to Qt 'plugins' folder. It helps to avoid definition of additional variable (QT_QPA_PLATFORM_PLUGIN_PATH) when staring sample.bat for qt samples;
- executable processing is extended in cmake procedure by providing 'EXECUTABLE_PROJECT' variable. Now we need not specify custom processing for DRAWEXE in occt_toolkit.cmake

samples/qt/FuncDemo/src/FILES

@@ -0,0 +1,28 @@
+BaseDriver.cpp
+BaseDriver.h
+CircleDriver.cpp
+CircleDriver.h
+ConeDriver.cpp
+ConeDriver.h
+CylinderDriver.cpp
+CylinderDriver.h
+edge.cpp
+edge.h
+FILES
+FThread.cpp
+FThread.h
+graphwidget.cpp
+graphwidget.h
+main.cpp
+mainwindow.cpp
+mainwindow.h
+node.cpp
+node.h
+PointDriver.cpp
+PointDriver.h
+PrismDriver.cpp
+PrismDriver.h
+ShapeSaverDriver.cpp
+ShapeSaverDriver.h
+SimpleDriver.cpp
+SimpleDriver.h