Added Qt sample OCCTOverview providing examples of use of OCCT API with relevant code and demonstration of results in the viewer.
Off-topic: some unused images are removed from dox/introduction/images/
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
