Restore previously-open documents on launch by default
This feature is on by default but can be turned off, as in Dolphin. The behavior is pretty much identical with one exception: in Dolphin, opening the app with a URL causes that URL to be appended to the existing set of tabs; with this change to Okular, doing this would create a fresh clean instance of Okular with the specified document, not opening any previously-open documents as well. We could consider doing the same thing for Okular, but I chose not to here because I thought it would be annoying in Okular, whereas it's apparently not annoying for Dolphin.
Edited by Nate Graham