CTest-based dashboard testing

The requests adds new CTest scripts for OpenCV dashboard testing, which includes:

* repository update;
* project configuration via CMake;
* building;
* testing;
* code coverage analysis;
* memory check analysis via valgrind;
* packaging;
* submitting results to remote server (currently disabled).

The new scripts will allow users to perform full OpenCV testing on their machines and send reports to a common place, for example CDash server (http://my.cdash.org/index.php). This can be used as an extension for current testing procedure to cover larger number of possible configurations (OS, compilers, features like CUDA, etc.).

For detailed information please refer to the [README](https://github.com/jet47/opencv/blob/45d07ba8287a32feef4c7279fbafaa4c98dfe446/ctest/README.md) file.