Add support for embedding image from RGB/BGR matrix

Example:
```python
from PIL import Image
import numpy as np
from orangecontrib.imageanalytics.image_embedder import ImageEmbedder

embedder = ImageEmbedder(model="squeezenet")
img = Image.open("img.jpg")
img_data = embedder([np.array(img)])
```

Start with the ImageEmbedder entry point in orangecontrib/imageanalytics/image_embedder.py and reproduce the provided NumPy RGB image example. Determine the expected RGB/BGR matrix input behavior; done means an image matrix can be passed to the embedder successfully, with coverage for the supported channel ordering if existing tests are found.

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