kcms/rules: replace dock/panel icon

The combobox for window type matching in the rules kcm currently uses
list-remove (represented by a minus sign) as its icon; while
semantically ill-fitting, it was visually a good match and breeze-icon-
theme does not have a dedicated panel icon. Recently however, the icon
was changed and now depicts a red X. This makes it a bad fit all-around
for its use in this kcm.

This change replaces it with another visually good fit that doesn't
match semantically, namely spinbox-decrease (also a minus sign), as a
temporary measure until a proper panel icon is ready (tracked in BUG
492341).

src/kcms/rules/rulesmodel.cpp

@@ -818,7 +818,7 @@ QList<OptionsModel::Data> RulesModel::windowTypesModelData() const
         {1 << NET::Normal, i18n("Normal window"), QIcon::fromTheme("window")},
         {1 << NET::Dialog, i18n("Dialog window"), QIcon::fromTheme("window-duplicate")},
         {1 << NET::Utility, i18n("Utility window"), QIcon::fromTheme("dialog-object-properties")},
-        {1 << NET::Dock, i18n("Dock (panel)"), QIcon::fromTheme("list-remove")},
+        {1 << NET::Dock, i18n("Dock (panel)"), QIcon::fromTheme("spinbox-decrease")}, // see bug 492341
         {1 << NET::Toolbar, i18n("Toolbar"), QIcon::fromTheme("tools")},
         {1 << NET::Menu, i18n("Torn-off menu"), QIcon::fromTheme("overflow-menu-left")},
         {1 << NET::Splash, i18n("Splash screen"), QIcon::fromTheme("embosstool")},