[MlMt] Notification opens new window

[John D. Muccigrosso]

When I click on a notification of a new message, MM2 opens a new inbox 
window with the message in the Preview pane at bottom.

Ideally it would show you the new message in whatever form you usually 
use. So, for me that would mean it would open the message in a new 
viewer window. Others might use the preview pane and so just have it be 
selected.

John