Adds blocks.go + blocks_test.go

[jacksonConrad]

blocks.go:

• adds helper functions that proxy the flowkit Services.Blocks API
• GetLatestBlock(), GetBlockAtHeight(), GetBlockById()
  blocks_test.go: happy paths for each added function

[coveralls]

Pull Request Test Coverage Report for Build 2111673718

• 12 of 12 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.3%) to 59.175%

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Totals
Change from base Build 2110376092:	0.3%
Covered Lines:	932
Relevant Lines:	1575

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💛 - Coveralls

[jacksonConrad]

@bjartek i added tests, though I'm not sure how necessary they are considering we are just proxying the flowkit Services.Blocks API.

I kept the helper functions simple. I figure if someone needs more, they can just use the overflow.Services APIs directly.

[bjartek]

Thanks! Merged!