Describe the bug
In CropForeground/CropForegroundd the user can request a margin around the foreground voxels. However, currently the margin is only correctly padded on the upper side of a dimension.

See:

To Reproduce

from monai.transforms import CropForeground
import numpy as np

transform = CropForeground(margin=2)
arr = np.eye(3)[np.newaxis, ...]
for i in range(3):
    inp = arr[:, i]
    res = transform(inp)
    print(inp, res.shape)
# [[1. 0. 0.]] (1, 3)
# [[0. 1. 0.]] (1, 4)
# [[0. 0. 1.]] (1, 5)

Expected behavior
The specified margin should be enforced by cropping or padding on both ends of a dimension.

Environment
Monai 0.8.0, but see Permalink above