Implement the DDS algorithm for spotpy

[bees4ever]

This is a new PR based on: https://github.com/thouska/spotpy/pull/185 where some mistakes are fixed.

[coveralls]

Pull Request Test Coverage Report for Build 659

• 250 of 270 (92.59%) changed or added relevant lines in 5 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 90.489%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
spotpy/algorithms/dds.py	128	136	94.12%
spotpy/unittests/test_dds.py	110	122	90.16%
<!--	Total:	250	270	92.59%	-->

Files with Coverage Reduction	New Missed Lines	%
spotpy/algorithms/rope.py	1	89.29%
<!--	Total:	1		-->

Totals
Change from base Build 654:	-0.1%
Covered Lines:	5214
Relevant Lines:	5762

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💛 - Coveralls

[thouska]

Super nice work! Thank you very much for this large contribution, I think this the DDS algorithm is ready to merge now, as it has proven to provide the same results as the original matlab version. Good job :)