refactor(directive): rename the directive

Before:
<countries></countries>

After:
<ghanoz-countries></ghanoz-countries>

Notes:
- Add more service to pluck out the country names
- Isolate the scope on directive
- To get the value of selected country name, listen on 'country.selected' event in your application controller, $scope.$on('country.selected', ...)
Merge branch 'refactor'