[Backport to 11.2] Cannot add component to empty nomarkup container

It's not possible to add a component to an empty container of type 'nomarkup'. Since all containers in a new project use the 'nomarkup' type by default (ESSENTIALS-1033), the net effect is that no components can be added anywhere in a new project.

This can be reproduced in the HAP on the 'Events' page, since the main container there is of type 'nomarkup':
1. edit the Hippo Acceptance Project channel
2. navigate to the 'Events' page
3. delete the 'Events List' component from the main container
4. add a new component to the main container

Expected: the main container show the new component
Actual: the new component is not added. The JavaScript console contains the following error:

TypeError: Cannot read property 'parentNode' of null
    at ContainerElement._removeSiblingsUntil (pageStructureElement.js:116)
    at ContainerElement.replaceDOM (pageStructureElement.js:101)
    at PageStructureService._updateContainer (pageStructure.service.js:333)
    at pageStructure.service.js:326
    at processQueue (angular.js:16383)
    at angular.js:16399
    at Scope.$eval (angular.js:17682)
    at Scope.$digest (angular.js:17495)
    at Scope.$apply (angular.js:17790)
    at done (angular.js:11831)