Enable alternatingRowColors for "Manage Cookie" dialog

Set editTriggers property to AllEditTriggers for easier editing.
Now a single mouse click can initiate item editing instead of double
clicking.

src/gui/cookiesdialog.ui

@@ -18,6 +18,12 @@
     <layout class="QHBoxLayout" name="horizontalLayout">
      <item>
       <widget class="QTreeView" name="treeView">
+       <property name="editTriggers">
+        <set>QAbstractItemView::AllEditTriggers</set>
+       </property>
+       <property name="alternatingRowColors">
+        <bool>true</bool>
+       </property>
        <property name="selectionMode">
         <enum>QAbstractItemView::ExtendedSelection</enum>
        </property>