Skip ErgoBox.id on JSON deserialization and build it from scratch

[greenhat]

Close #53

Todo:

• ErgoBox serialization;
• ErgoBox.id hash calculation (import blake2b256 impl);
• skip id on JSON deserialization and build it from scratch after all fields are deserialized;

[coveralls]

Pull Request Test Coverage Report for Build 343

• 92 of 100 (92.0%) changed or added relevant lines in 7 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+1.4%) to 73.97%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
sigma-tree/src/chain/address.rs	0	1	0.0%
sigma-tree/src/serialization/ergo_box.rs	43	45	95.56%
sigma-tree/src/chain/ergo_box.rs	40	45	88.89%

Files with Coverage Reduction	New Missed Lines	%
sigma-tree/src/ergo_tree.rs	2	88.37%

Totals
Change from base Build 333:	1.4%
Covered Lines:	790
Relevant Lines:	1068

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💛 - Coveralls