Consistent document icon

[maltem-za]

The icon for documents in the annotate module (within the latch) changes to an open book when a document is opened. It would probably be better to be consistent and not change the icon based on state, especially as we don't do this with other resource icons, it only relates to the currently active document tab, the window for not having a document open is very small, and there are sufficient other visual cues to let the user know that the document is open (radio button in latch, document tab title).

Related: #274