Some tools for working with spreadsheets (C4-1088)

[netsettler]

This is a preliminary cut at some tools for parsing excel workbooks.

[coveralls]

Pull Request Test Coverage Report for Build 5958607573

• 156 of 160 (97.5%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.3%) to 78.039%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
dcicutils/sheet_utils.py	156	160	97.5%
<!--	Total:	156	160	97.5%	-->

Totals
Change from base Build 5943632943:	0.3%
Covered Lines:	8390
Relevant Lines:	10751

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💛 - Coveralls