Allow to override format methods in service

[bobisjan]

• I am on the latest ember-intl version
• I have searched the issues of this repo and believe that this is not a duplicate

Steps to Reproduce

1. Add own service app/services/intl.js
2. Subclass service from ember-intl
3. Override any of the format* methods

import EmberIntl from 'ember-intl/services/intl';

export default class IntlService extends EmberIntl {

  formatDate(date, options) {
    // do something custom
    return super.formatDate(...arguments)
  }
}

4. service.formatDate() calls original method-as-property instead of the custom method 💥

I'm not sure if this is intentional or format* methods should be defined as prototype methods on class to allow/fix standard/expected behaviour?

[ijlee2]

Will close this issue. Rather than inheritance, end-developers are encouraged to inject the intl service (composition).