[applets/folder] Add icons to icon properties menu items

The menu items in the desktop context menu section Icons now all have icons.

I also wanted to change the "Arrange In" and "Align" icons depending on what is currently selected. The problem is that something like

if (arrangement() == 0) {
    m_arrangementMenu->setIcon(QIcon::fromTheme(QStringLiteral("object-rows")));
}

lets Plasma still compile, but not start up anymore. @teams/vdg