Glorious merge of code coverage and testem configuration

[Antranig Basman]

I'm happy to report the merge of a major and significantly useful pull request 
https://github.com/fluid-project/infusion/pull/822 from Tony Atkins which adds long-awaited and much needed 
code coverage and testem drivers to Infusion. As well as providing amalgamated coverage reports derived from 
both our browser and node-based tests, it provides an all-in-one testem driver that will execute all such 
tests in all available browsers and node.js.

This will be invaluable to us in CI, and will shortly be a part of the automated builds run on each pull 
request. It will be important in future reviews to ensure that new work has good coverage, coverage of 
existing work does not degrade, and that we should work steadily to bring areas of old implementation up to 
reasonable standards of coverage (e.g. branch coverage of about 90% represents a reasonable baseline. For 
example we have interestingly poor coverage of jquery.keyboard-a11y.js via automated tests.

The coverage reports are generated automatically by running "npm test" and can be accessed in the newly 
generated "reports" directory. Machine-readable summaries of the coverage are produced in "coverage".

Let us all join in congratulating ADTKINS on almost a year of steering this pull request to a successful 
conclusion. Similar work is in progress for GPII projects but looks like it will be blocked by moving those 
projects over to a "monorepo" structure.

Cheers,

Antranig