Add istanbul
Add coverage with istanbul
Add coverage folder in gitignore file
Add codeclimate-test-reporter installation
Add codeclimate coverage in travis-ci config
Add codeclimate badges in readme file
Merge branch 'add-codeclimate' into develop

* add-codeclimate:
  Add codeclimate badges in readme file
  Add codeclimate coverage in travis-ci config
  Add codeclimate-test-reporter installation
  Add coverage folder in gitignore file
  Add coverage with istanbul
  Add istanbul