add istanbul code coverage to unit test runner

% npm install -g karma-coverage --save-dev
% npm install karma-coverage

c.f.
http://stackoverflow.com/questions/18069865/unable-to-run-coverage-with-
karma

http://ariya.ofilabs.com/2013/10/code-coverage-of-jasmine-tests-using-is
tanbul-and-karma.html

open coverage/*/index.html to see report