Update Fragment blueprint to use class instead of extend

[Gorzas]

As Ember team is deprecating EmberObjects and it's recommending to use ES6 classes, I think we can update the Fragment blueprint to follow this syntax:

import MF from 'ember-data-model-fragments';

export default class <% name %> extends MF.Fragment {
 <% attrs %>
}

What do you think? I may leave a PR with my proposal.

[patocallaghan]

@Gorzas I think this is a good idea. It might be worth doing to get it into the 5.0.0 beta release. It might also be better to use the specific Fragment import (similar to the updated Ember Data package imports)

import Fragment from 'ember-data-model-fragments/fragment';

export default class <% name %> extends Fragment {
 <% attrs %>
}

[Gorzas]

@patocallaghan Yes, I think it's better this way. Made the changes 😄.