Update this addon to a more modern approach

[kiwiupover]

1. Remove the need to use Ember directly.
2. Use ember-auto-import to use mockdate.
3. Update ember-cli and ember to the latest version.
4. Added github actions to run CI.
5. Update tests to use modern ember idioms.

[jrjohnson]

It seems like backburner tries to call this as a function, so now should be passed here without calling it.

Suggested change

	trySet(run, 'backburner._platform.now', originalDate.now());
	trySet(run, 'backburner._platform.now', originalDate.now);

[kiwi-josh]

Abit has changed since this PR was opened, therefore I've opened another one that is heavily inspired by these changes, but is up to date against the last ember version (4.4)
#35

(I've also made sure this comment is taken into account: #30 (comment))