Use more appropriate icon for "Create New" action

Right now this action is using the "document-new" icon, which depicts creating a new file. This is inaccurate, as the menu provides options for creating more than just files: it has one option to create folders and three for creating different types of links. In fact, depending on the set of installed software, there may not be any options to create new documents at all!

To fix this, the icon would need to be made either more specific or more generic.

There is no such icon that depicts being able to create a folder, a document, or a link; such a thing is too specific to be able to represent with a small icon. So our only real option is to use a more generic icon.

This commit does that.

BEFORE	AFTER

cc @teams/vdg