Adding get_random_seed(), and adding func calc_quantile_crps()

[WenjieDu]

What does this PR do?

1. fixing Need a func to calc CRPS for evaluating imputation from probabilistic models like CSDI #259;
2. adding get_random_see();

Before submitting

• Was this discussed/approved via a GitHub issue? Please add a link to it if that's the case.
• I have commented my code, particularly in hard-to-understand areas.
• I have written necessary tests and already run them locally.

[coveralls]

Pull Request Test Coverage Report for Build 7144108583

• 102 of 156 (65.38%) changed or added relevant lines in 15 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.6%) to 83.043%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pypots/utils/metrics/classification.py	15	25	60.0%
pypots/utils/metrics/clustering.py	26	44	59.09%
pypots/utils/metrics/error.py	34	60	56.67%

Totals
Change from base Build 7125620794:	-0.6%
Covered Lines:	4809
Relevant Lines:	5791

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💛 - Coveralls