CMS-4064 Remove Site Templates - enable special rendering of system.page-templates
Replaced all instanceof usages with api.ObjectHelper.iFrameSafeInstanceOf, since they are not working on objects created in another iframe. This fixed at least one bug.

If content has no page template or controller, then Content.page must stay as null. This was not adhered to, causing a Page to be created if saving a content no page but with default page template.

Removed getLayoutRegions from PortalContext