Quick patch that fixes the `EnableValidationWithCallback` sample:
There's no `str()` method here, should use `c_str()`;
*but* also, you can print the std::string directly to `std::cout`.
Patches remove `.str()` from printing line when WIN32 is not defined.
* Add samples SecondaryCommandBuffer and SeparateImageSampler.
+ made some helper functions more explicit.
* Add sample Template, some generalizations in utils, some minor improvements in various samples.
