Don't scroll on initial load

[lolmaus]

Hi, thanks for the great addon!

With FastBoot, the user is able to scroll down the static HTML version of the app.

When the app rehydrates, ember-router-scroll resets scrolling, producing jerky behavior.

[lolmaus]

I've found the isFirstLoad property. It is read here, but it does not set up to prevent scrolling:

ember-router-scroll/addon/index.js

Lines 146 to 148 in d6cc035

	if (get(this, 'service.isFirstLoad')) {
	get(this, 'service').unsetFirstLoad();
	}

[lolmaus]

This ugly hack resolves the issue for me:

    this.routerScroll.set('preserveScrollPosition', true);

    later(this, function () {
        this.routerScroll.set('preserveScrollPosition', false);
    }, 1000);

...in application route's beforeModel hook.

[snewcomer]

@lolmaus 👍 Do you see an improvement that could be added here? Thx for the issue btw!