G-API: Introduced Security Barrier & Interactive Face Detection samples

* G-API-NG/Samples: Added samples & relevant changes

- Security barrier camera sample
- Age/Gender/Emotions recognition sample
- GIEBackend now loads CPU extension libraries
- A couple of API-level workarounds added to deal with cv::Mat/Blob conversions

* G-API-NG/Samples: removed HAVE_INF_ENGINE remnants