IEPlugin removed from upcoming OpenVINO versions

[benhoff]

Currently the Auto Annotation app uses the class IEPlugin from openvino. See here: https://github.com/opencv/cvat/blob/76280be4ad4c6143533b6a3960a429d33e7f10a8/cvat/apps/auto_annotation/inference_engine.py#L5

In upcoming versions of OpenVINO, this class has been removed. See here for more information:
openvinotoolkit/openvino#920

This will cause new installations of CVAT to break when using newer versions of OpenVINO with an error of:
ImportError: cannot import name 'IEPlugin' from 'openvino.inference_engine'

I believe the core of this is already handled in this commit: 1408443

Probably need to put a try/catch around IEPlugin to degrade gracefully.

[benhoff]

Related to OpenVINO API changes:

cvat/apps/auto_annotation/model_loader.py:28: DeprecationWarning: 'inputs' property of IENetwork class is deprecated. To access DataPtrs user need to use 'input_data' property of InputInfoPtr objects which can be accessed by 'input_info' property.
  iter_inputs = iter(network.inputs

[nmanovic]

Should be fixed by #1767