Changes PetaPoco UOW to use a Queue instead of trying to order by a date which even in ticks is sometimes the same. Changes some content ext to accept the service it needs instead of relying on the app ctx singleton and obsoletes others. Fixes ContentBase.ContentTypeId to check if the Id has been set on it's true ContentTypeBase which is required with the new foreign key to insert entities (this was actually a bug without the foreign key).  Updates media/content services with paging to use parameters correctly. Fixes tests.
Merge branch '7.2.0' of https://github.com/umbraco/Umbraco-CMS into 7.2.0