Create/update table from schema

[gfr10598]

This adds functionality to create or update a bigquery table.

Let me know if you think this would be better separated into two separate functions.

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This change is 

[coveralls]

Pull Request Test Coverage Report for Build 456

• 37 of 51 (72.55%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.4%) to 77.778%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
bqx/schema.go	37	51	72.55%
<!--	Total:	37	51	72.55%	-->

Totals
Change from base Build 452:	-0.4%
Covered Lines:	630
Relevant Lines:	810

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 492

• 64 of 72 (88.89%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.9%) to 79.036%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
bqx/schema.go	64	72	88.89%
<!--	Total:	64	72	88.89%	-->

Totals
Change from base Build 452:	0.9%
Covered Lines:	656
Relevant Lines:	830

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💛 - Coveralls