This moves the preferences to an external window instead of
using a perspective within the parent window. This useful for
couple of reasons:

 * It allows us to use the preferences outside of the workbench
   such as during the greeter phase.
 * It allows us to destroy widgets when they aren't visible.
   There are lots created in preferences, so this is a sort of
   nice thing from a memory usage standpoint.
 * Reduce the time it takes to open a project since it would
   add the preferences as part of that phase.