* ngraph and inference-engine parts
* add priorbox_8 python api
* remove 'PriorBoxAttrs' and 'PriorBox' from outside of opset namespace
* add common nGraph transformation 'ConvertPriorBox8To0'
* remove redundant alias of PriorBox::Attributes
* use new Tensor api for evaluate method
* change v0operation back to the former api, pass Attribute structure to the reference implement
* use new Tensor api for constant_fold
* add support for dynamic shapes of constant_fold new Tensor api
* fix Node 'create temp tensors' issue when shape==0'
* revert to 'HostTensor' api for PriorBox8
* Apply suggestions from code review and 'template_plugin reference' testcase replaced 'backend INTERPRETER' testcase
* transformation part Apply suggestions from code review
* python init file updated for opset8
* keep backward compatibility to fix CI issue
* rebase to new structure of OpenVINO repo
* revert 'thirdparty/onednn_gpu' mistake changes