Allow configuring default preferences for Super Admin and Guest users

#-# [Since 12.2RC1]
#-# Define preferences for the SuperAdmin user.
#-#
#-# The format is:
#-# user.preferences.superadmin.<preference name> = <value>
#-#
#-# Examples:
#-# user.preferences.superadmin.displayHiddenDocuments = 0
#-# user.preferences.superadmin.editor = Wysiwyg

#-# [Since 12.2RC1]
#-# Define preferences for the Guest user.
#-#
#-# The format is:
#-# user.preferences.guest.<preference name> = <value>
#-#
#-# Examples:
#-# user.preferences.guest.displayHiddenDocuments = 1
#-# user.preferences.guest.editor = Text