Separate boards settings from card creation

* Move GitHub repository url and heroku app name to Board
* Move  to Board
@exalted The only workaround I can think of would be to extract a variable:

```ruby
permitted_parameters = [:whatever, :whatever]
params.require(:board).permit(permitted_parameters)
```

This doesn't help to clarify the intent of the method, nor removes any duplication whatsoever. Therefore I'd say to ignore @houndci suggestions, and go on with our lives :wink: