Tests for importing PNG images

[axmat]

Is your feature request related to a problem? Please describe.
The MemRef container has the ability to import images using libPNG or OpenCV. Currently there are no tests for importing RGB images.

Describe the solution you'd like
We should:

1. Generate a PNG image.
2. Read the image using OpenCV and libPNG and create a MemRef container.
3. Compare the memref and the generated image pixel by pixel.
4. Add tests for importing images in UnitTests/TestContainer.cpp.
   The following script for generating random PNG images using PIL can be used as a starting point https://github.com/axmat/mlir-inference/blob/master/scripts/gen-images.py