Remove SciPy as a development dependency

[IvanIsCoding]

This PR removes SciPy as a development dependency. Instead of relying on NetworkX's new implementation based on SciPy, this introduced forked code from NetworkX's old pure Python implementation.

I added NetworkX's BSD-3 license at the top of the files. We have already done similar for the visualization module in the past.

Partially motivated by #1220. But it is nice to test the hits and pagerank methods in architectures that previously skipped the test before

[coveralls]

Pull Request Test Coverage Report for Build 9590028523

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.02%) to 95.844%

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Files with Coverage Reduction	New Missed Lines	%
src/iterators.rs	3	75.15%

Totals
Change from base Build 9589302565:	-0.02%
Covered Lines:	17410
Relevant Lines:	18165

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💛 - Coveralls

[mtreinish]

This looks fine to me, I like removing scipy as a test dependency, just a comment inline about the exceptions.

[mtreinish]

Thanks for the quick update

[coveralls]

Pull Request Test Coverage Report for Build 9620377450

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.02%) to 95.863%

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Files with Coverage Reduction	New Missed Lines	%
src/iterators.rs	3	75.89%

Totals
Change from base Build 9620375454:	-0.02%
Covered Lines:	17589
Relevant Lines:	18348

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💛 - Coveralls