Changed both Preferences classes to use their their package & class to uniquely store items in preferences.
Changed SelectedPaths to save and load multiple reference paths.
Added code to set the window location and ensure that the window is within the bounds of a screen. (This needs to be tested more thoroughly but my dev environment only has one screen.)
Implemented a basic HTML DiffReport based on the output from a FileDifferentiator object. (As discussed, we will eventually have an object that creates reports based on the results from the UI.)
Added code to cleanup the Preferences tests by either setting the values back to their previous state or clearing them if they did not previously exist.
Added a unit test for the DiffReport.