Fixes U4-2822 Datepicker throws "Specified cast is not valid" when saving through API
Refactoring how DeleteVersion and DeleteVersions is used in the Content- and MediaRepository, so we ensure that the latest version is never deleted. Worse case would have been an incomplete content node, which we want to avoid. So better to have a fail safe way of deleting versions, and use the regular Delete method for deleting the latest version.
Fixing broken Publishing test after the service and repository tests are probably setup.
Merge branch '6.2.0' of https://github.com/umbraco/Umbraco-CMS into 6.2.0