No GPU acceleration in torch backend

**Describe the bug**
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It seems like all parameters of the torch-based normalizers are hard coded as tensors on CPUs and therefore there are no GPU acceleration at all unless one explicitly move the target, input, and all stain vectors to GPU devices.
Might be an easier way to fix this by making your torch normalizer also extend from torch.nn.Modules like all torchvision's transformation API does, and use `register_buffer` to store parameters and the whole normalizer object can be moved to specified device as whole.

**To Reproduce**
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**Expected behavior**
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**Desktop (please complete the following information):**
- OS: [e.g. Ubuntu, Windows, macOS]
- Version [e.g. 20.04, 10, Catalina]