Embroider compatibility

[dbendaou]

It seems that the addon cannot be run with Embroider.
Indeed, I have the following error in my test

I would say that it's caused by the fact that we're renaming the import path of the addon from
ember-power-calendar-date-fns to ember-power-calendar-util but I'm not sure how we could fix that

[Techn1x]

I think a great first step to upgrading this plugin would be to use the moment & luxon plugins as a guide, which are much more up to date (eg ember-auto-import v2), and also seem way simpler (eg only exporting a single index.js and using broccoli-funnel to move to xxx-utils, no use of string-replace)
https://github.com/cibernox/ember-power-calendar-moment
https://github.com/cibernox/ember-power-calendar-luxon

cc @cibernox

[Techn1x]

cc @makepanic if you're still around