Add about dialog to File menu of the connection manager.

Make the contents of the dialog more accurate and include a link to the releasenotes file.

pglab/ConnectionManagerWindow.ui

@@ -26,13 +26,14 @@
      <x>0</x>
      <y>0</y>
      <width>413</width>
-     <height>30</height>
+     <height>29</height>
     </rect>
    </property>
    <widget class="QMenu" name="menuFile">
     <property name="title">
      <string>Fi&amp;le</string>
     </property>
+    <addaction name="actionAbout"/>
     <addaction name="actionQuit_application"/>
    </widget>
    <addaction name="menuFile"/>
@@ -164,6 +165,16 @@ QToolButton {
     <string>Configure copy</string>
    </property>
   </action>
+  <action name="actionAbout">
+   <property name="icon">
+    <iconset>
+     <normalon>:/icons/about.png</normalon>
+    </iconset>
+   </property>
+   <property name="text">
+    <string>About</string>
+   </property>
+  </action>
  </widget>
  <resources>
   <include location="resources.qrc"/>