Merge pull request #16555 from dmatveev:dm/ocv_blog_sample

Merge pull request #16555 from dmatveev:dm/ocv_blog_sample

* G-API/Samples: Added a simple "privacy masking camera" sample

The main idea is to host this code for an opencv.org blog post only

* G-API/Samples: Modified privacy masking camera code to look better for the post

* G-API/Samples: fix Windows (MSVC) support in Privacy Masking Camera

* G-API/Samples: Addressed the majority of review comments in PMC

* G-API/Samples: Use TickMeter to measure time + more info in cmd options

* G-API/Samples: fix yet another Windows warning in PMC

* G-API/Samples: Fix wording in PMC cmd arg parameters

* Fix wording, again

* G-API/Samples: Fix PMC cmd-line arguments, again