Fixes: U4-4634 Image preview in Media is stretched
Merge branch '7.1.5' of https://github.com/umbraco/Umbraco-CMS into 7.1.5
Updates some naming conventions and code formatting
#U4-5258 Fixed

RelationService AreRelated should accepts two entity IDs and a relationTypeAlias
#U4-5337 fixed Due in version: 7.1.5,6.2.2

Too easy to lock yourself out of the backoffice