Fix issue #15.
Just replace the west tree by using CellTree, resulting in issue #16 & #17

git-svn-id: https://svn.apache.org/repos/asf/james/hupa/trunk@1522217 13f79535-47bb-0310-9956-ffa450edef68
fixed issue #16
[Issue 16]click events should be attached to the CellTree so that the messages list can display at the main panel.

git-svn-id: https://svn.apache.org/repos/asf/james/hupa/trunk@1522218 13f79535-47bb-0310-9956-ffa450edef68