Dichotomous products are now added to cart when their checkbox is clicked

[JDSalisbury]

We tried

[alexjamesmalcolm]

I believe this fixes #74

[coveralls]

Pull Request Test Coverage Report for Build 493

• 0 of 0 (NaN%) changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 89.841%

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Totals
Change from base Build 491:	0.0%
Covered Lines:	283
Relevant Lines:	315

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💛 - Coveralls