add test/coverage to .gitignore

 test/coverage is a directory containing Code-Coverage information
 on karma/mocha unit-tests.

 Given that we plan to refactor a whole chunk of boomerang post setting
 up all the unit-tests it is important to get all code-paths to the
 unit-tests
Remove unnecessary parts of karma-runner config from Gruntfile.js

 Most none grunt-task related configuration is moved to karma.config.js

 The goal is to remove clutter from Gruntfile.js
Add "karma-coverage" for unit-test code-coverage to devDepencies

 Code coverage is relevant to for refactoring purposes see
 bluesmoon/boomerang issue #40 for more information.
Fix indentation and point to built version of boomerang.js
Extend test coverage