Add close option for documents as action button

Acceptance criteria

1. A new button is added to the top navigation of a document in edit-mode when within the content perspective: Close (see the attached image for how this button should look and where it should be positioned).

2. This new button functions in exactly the same way as if a user had clicked the 'X' button on a document tab at the bottom of the screen (see attached screenshot).

• if the user has made changes to the document and they click the new button a dialogue appears
• if the user has not made changes to the document no dialogue appears and the document is closed

[Carolien] Consider adding a button to discard changes in preview without publishing.