TensorRT8 support (Plugin Migration to IPluginV2 & IPluginV2Ext )

New Features:

Added support for TensorRT 8 through IPluginV2(activation Layers) && IPluginV2Ext(all other plugins) along the lines of how they are in NVIDIA's open source TensorRT repository ,Updated C++ version to 14 and Tested it on both Windows 10(MSVC 16) and Ubuntu-20.04(gcc-9.3 and clang-11) with CUDA-11.3(CUDNN 8.2.1 and TENSORRT 8.0.3) and CUDA-10.2(CUDNN 8.1.1 and TENSORRT 7.2.3) with almost all the networks in the test folder with both INT8 and FP32 (unfortunately my hardware doesn't support FP16)
Updated Docker to CUDA-11.3
Added CUDA arch auto-detect to CMakeLists.txt and option for OpenCV cuda contrib from CMakeLists.txt instead of uncommenting it from DetectionNN.h
Shelfnet now works on cuda 11.x and on windows thanks to @mive93

API Changes:

Modified DetectionNN::init to include config and name files for darknet based networks (null for centernet and mobilenet)
Plugins are created using a combination of pluginRegistry and directly depending on the type of plugin

Known Issues:

Severe slump in fps ,if opencv is built with QT enabled both on windows(410 native vs 192 qt) and linux(440 gtk vs 330 qt) for yolo4tiny on a gtx 1070
Centernet doesn't work properly on WSL2 (with gpu access)

ceccocats / tkDNN