Alter SimpleBoxSelector algo to sort inputs by target tokens;

[greenhat]

Close #174

Summary

• Sort inputs by target tokens amount, putting inputs with largets target tokens first.
• While going through sorted inputs having only target tokens missing skip the input if it does not have any of the target tokens.

[coveralls]

Pull Request Test Coverage Report for Build 496425880

• 57 of 62 (91.94%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.04%) to 84.434%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
ergo-lib/src/wallet/box_selector/simple.rs	57	62	91.94%

Files with Coverage Reduction	New Missed Lines	%
ergo-lib/src/types/scontext.rs	1	93.33%
ergo-lib/src/wallet/box_selector/simple.rs	1	95.9%

Totals
Change from base Build 493074853:	-0.04%
Covered Lines:	3477
Relevant Lines:	4118

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💛 - Coveralls