Implement PyTorch deep learning base detector and utility functions.

[RaymondY]

All Submissions Basics:

• [x] Have you followed the guidelines in our Contributing document?
• [x] Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• [x] Have you checked all Issues to tie the PR to a specific one?

All Submissions Cores:

• [x] Have you added an explanation of what your changes do and why you'd like us to include them?
• [x] Have you written new tests for your core changes, as applicable?
• [x] Have you successfully run tests with your changes locally?
• [x] Does your submission have appropriate code coverage? The cutoff threshold is 95% by Coversall.

New Model Submissions:

• [x] Have you created a .py in ~/pyod/models/?
• [x] Have you created a test_.py in ~/pyod/test/?
• [x] Have you lint your code locally prior to submission?

[coveralls]

Pull Request Test Coverage Report for Build 9314657234

Details

• 425 of 440 (96.59%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 93.931%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pyod/test/test_torch_utility.py	118	119	99.16%
pyod/utils/torch_utility.py	88	89	98.88%
pyod/test/test_base_dl.py	98	104	94.23%
pyod/models/base_dl.py	121	128	94.53%
<!--	Total:	425	440	96.59%	-->

Totals
Change from base Build 9179723190:	0.1%
Covered Lines:	9395
Relevant Lines:	10002

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💛 - Coveralls