Refactor checkbox component

[matheuspoleza]

style guide:

• https://github.com/rwwagner90/angular-styleguide-es6

notes:

• add documentation code with djeni
• use templateUrl and create a template file
• use $scope on controller rather than this or self

[matheuspoleza]

@m0t0r I will assume this task. I can?

[m0t0r]

@matheuspoleza we already have #56 for it