Add Server, Client, and Models Package

[patrick-ogrady]

Motivation

To implement a Rosetta server, it was necessary to setup your own codegen toolchain and keep it working across interface updates. This was a drain on engineering resources for anyone working on a server.

Secondly, there were no examples demonstrating how to use the different packages.

Solution

Create a server package that makes it easy to write a Rosetta server, break apart the Rosetta models into a separate package for anyone looking to build their own server, and add a ton of examples.

[coveralls]

Pull Request Test Coverage Report for Build 384

• 113 of 122 (92.62%) changed or added relevant lines in 5 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+3.9%) to 82.889%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
asserter/request.go	71	73	97.26%
asserter/block.go	25	28	89.29%
asserter/network.go	12	16	75.0%

Totals
Change from base Build 158:	3.9%
Covered Lines:	373
Relevant Lines:	450

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💛 - Coveralls

[etscrivner]

Big improvements here 👍