Updated room sorting

Change the LastActivity sort order to Activity and update to a more flexible way of sorting based on an order from model roles.
Add options to actually switch between Alphabetical and Activity

Based on some old work by @tdfischer 

implements #103

src/neochatconfig.kcfg

@@ -118,6 +118,10 @@
       <label>Save the collapsed state of the room list</label>
       <default>false</default>
     </entry>
+    <entry name="SortOrder" type="int">
+      <label>The sort order for the rooms in the list.</label>
+      <default>1</default>
+    </entry>
   </group>
   <group name="NetworkProxy">
     <entry name="ProxyType" type="Enum">