Add rel='canonical' support

closes #1341
- Added canonical link to header using ghost_head helper.
Merge pull request #1388 from germanrcuriel/add-canonical-support

Add rel='canonical' support
Add Coverage report for Unit and Integration tests

issue #361
- Added shell:coverage task to generate coverage report
- Registered test-coverage Grunt task as shortcut of shell:coverage
- Added coverage files to .gitignore
- Added require-cli and blanket to package.json