Updates to include returning the next step in sequence
Merge branch '7.1.0-installer' of https://github.com/umbraco/Umbraco-CMS into 7.1.0-installer

Conflicts:
	src/Umbraco.Web.UI.Client/src/installer/installer.service.js
	src/Umbraco.Web/Install/Controllers/InstallApiController.cs
Gets the installer steps working nicely and returning the next step to execute which now displays the current step details correctly and dequeues steps that are not required after the previous one has executed.