* G-API: Introduce a new gapi::infer2 overload + gaze estimation sample
* G-API/infer2: Introduced static type checking for infer2
- Also added extra tests on the type check routine
* G-API/infer2: Addressed self-review comments in the sample app
- Also fix build on Linux;
* G-API/infer2: Remove incorrect SetLayout(HWC) + dead code
- Also fixed comments in the backend
* G-API/infer2: Continue with self-review
- Fix warnings/compile errors in gaze estimation
- Dropped the use of RTTI (VectorRef::holds()) from the giebackend
- Replaced it with a trait-based enums for GArray<T> and std::vector<T>
- The enums and traits are temporary and need to be unified with
the S11N when it comes
* G-API/infer2: Final self-review items
- Refactored ROIList test to cover 70% for infer<> and infer2<>;
- Fixed the model data discovery routine to be compatible with new
OpenVINO;
- Hopefully fixed the final issues (warnings) with the sample.
* G-API/infer2: address review problems
- Fixed typo in comments;
- Fixed public (Doxygen) comment on GArray<GMat> input case for infer2;
- Made model lookup more flexible to allow new & old OMZ dir layouts.
* G-API/infer2: Change the model paths again
* G-API/infer2: Change the lookup path for test data
* G-API/infer2: use randu instead of imread. CI war is over
- reworked variant::operator(T&&) and varaint::variant(T&&) to be more
concise and signature accurate with C++17 specification
- restricted cv::detail::OpaqueRef::OpaqueRef(T&&) to not substitute
copy/move ctors
- moved common additions to C++11 version of std <type_traits> to
separte header
