[platform-ui-dev] Saving preferences

[Randy_Giffen@xxxxxxx]

Preference pages which use plugin preference stores should save the state of these stores in their performOK() method.
This ensures that the preference changes are not lost if the workbench fails to shutdown properly.

There is a method on Plugin to perform the save (which only does work if the store has unsaved state).
For example:         
        ReadmePlugin.getDefault().savePluginPreferences();