add search & display of available teachers&crooms

    add a dialog when clicking search button
    add methods to DAOs to find available teachers & crooms
    add methods to presenter, controller & model to do the job
    change date spinner of LevelManagmentForm to include the time
    add UserObjectButtonModel to attach any obj to a button
fix: pluralize getGroup() in Promo bean
fix hot renderer detail

    in ClassBasedDDR, if obj is null, don't call obj.toString()...
    show "Whole promo" when group id is 0
add group selection when choosing a session to add

    add a JComboBox to select group (promo is a 'fake' group w/ id=0)
    add presenter, model & controller methods to do the job
    add method in DAO to check id the group is available (false when
    week-end of course...)
fix homogeneity in native queries params
fix racism towards native queries...

   put them in head of beans just as classic jpql queries