Add Coverage report for Unit tests

issue #361
- Added shell:jscoverage task to convert library folder to generate coverage report with mocha
- Added shell:mocha_unit_coverage task to generate unit test coverage report
- Added shell:mocha_integration_coverage task to generate integration test coverage report
- Added clean:jscoverage task to remove converted folder when finished
- Registered test-coverage Grunt task to include all the above
- Added coverage files to .gitignore