Making the wmselectdialog somewhat bigger

it was fucking ugly (really) and not readable. 600x400 should work fine even
on ancient devices with 1024x600

Author: agaida

lxqt-session/src/wmselectdialog.ui

@@ -6,8 +6,8 @@
    <rect>
     <x>0</x>
     <y>0</y>
-    <width>352</width>
-    <height>276</height>
+    <width>600</width>
+    <height>400</height>
    </rect>
   </property>
   <property name="windowTitle">