Create new content by template on admin ui

[tusmester]

When a user creates a new content, we should provide a way for them to select a content template if there is one for the type.

Possibilities

1. directly from the New menu: add template options to the New menu, same way as in SN6
   • PRO
     • more prominent choice, cannot miss
     • the user would see the fields filled with default values
2. on the Create content page: somewhere in the header of the New page. A dropdown with the templates, or a dialog?
   • CON: what happens if the user changes the template in the header?

When a template is selected, the POST request should contain the template name and the new content should be created by the template. The backend is already capable of this.