Adds new features, based on amino acid swaps

[cbaakman]

• delta size
• delta charge
• delta polarity
• delta hydrogen bond acceptors & donors

[coveralls]

Pull Request Test Coverage Report for Build 3218469423

• 132 of 134 (98.51%) changed or added relevant lines in 6 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.4%) to 76.205%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
deeprank/features/amino_acid_swap.py	34	35	97.14%
deeprank/features/neighbour_profile.py	0	1	0.0%

Files with Coverage Reduction	New Missed Lines	%
deeprank/models/metrics.py	3	92.77%

Totals
Change from base Build 2971424162:	0.4%
Covered Lines:	3084
Relevant Lines:	4047

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💛 - Coveralls