Add test coverage reporting

[sathomas]

No description provided.

[sathomas]

The browser-based testing (grunt serve:test) is working sweetly, but I'm getting lost in the node black hole trying to make it work from the command line (grunt test). Feel free to try your own luck if you like.

[sathomas]

Nice update @stuartf. I've tried to build on this by adding support for coveralls.io, but I think we're out of luck. It seems like grunt-blanket-mocha can't generate the .lcov format files that coveralls.io requires. I'm basing that conclusion on my own experiments as well as a couple of open issues on the plugin's repo. If you see an easy way to add this, feel free. Otherwise, we can just remove the coveralls.io stuff and rely on the standard unit tests with code coverage thresholds to catch any problems.