Shared App IDs?

For example the Facebook services each use their own declared App ID:

`facebookApplicationId = services.facebookFollowButton?.applicationId ? '266367676718271'`

versus a single Facebook App ID, something like this:

`facebookApplicationId = services.fbAppId ? '266367676718271`

and also having these IDs global within the scope of the plugin versus declared every time like my question from #6
