Fix for U4-4493

Makes it possible to go back if you don't want to customize.

src/Umbraco.Web.UI.Client/src/installer/steps/database.html

@@ -104,6 +104,8 @@
 				<div class="controls">
 					<input type="submit" ng-disabled="myForm.$invalid || checking"  
 						value="Continue" class="btn btn-success" />
+
+						<button class="btn" ng-click="restart()">Go back</button>
                     
 					    <span class="inline-help" ng-if="checking" ng-animate="'fade'">
 	                    	Validating your database connection...