upgrade to Rails 4

* starts using strong_parameters, removing `attr_accessible` from models
* wrap all scopes within a lambda
* symbolize all keys for `APP_CONFIG`
* rewrite `wysiwyg_field` to fit into the Rails 4 way of building HTML tags for forms
* replace `update_attributes` with `update`
* remove the uses of `scoped` and `all` when not necessary
rewrite many specs

* use `specify` instead of `it` where it reads better
* remove `assigns()` tests that didn't actually test any functionality (the instance variable tests will be also replaced by full stack integration tests in the future)"