Merge `page-title` and `page-title-list` services?

[bertdeblock]

A while ago, a page-title service was introduced as a means to have a public titleDidUpdate hook, and also because the entire page-title-list service was/is considered private. I would like to suggest to have a single page-title service and document what's private and what's public instead. I think it would make the implementation a little easier and it would make using ember-page-title with engines less awkward, because at the moment you have to define the name of the page-title-list service to make it work properly: https://github.com/ember-cli/ember-page-title/issues/112#issuecomment-809939107

[raido]

This is doable. Why we didn't do it, when we introduced page-title public service, was because this is a breaking change and it did not seem feasible to bump major in that point of time.

Additionally since this addon is included by default, we need to consider effects of bumping up a major in between minor ember-cli versions.

We should probably begin with deprecations first.

[bertdeblock]

Can we include this as part of the v8 release? I don't think it's worth the time to introduce a deprecation for this. AFAICT, the only user change that's needed is to rename page-title-list to page-title?

[knownasilya]

@bertdeblock can you submit a pr?