MDL-9629 Changed grade_item.gradetype default to 1, added GRADE_TYPE_NONE constant...

MDL-9629 Changed grade_item.gradetype default to 1, added GRADE_TYPE_NONE constant = 0, incrementing existing constants by 1. Set up auto-generation of idnumber for grade_item if itemmodule and iteminstance are set, only a temporary stub if they are not set (must be replaced by correct generation code). New category form now has server-side validation (not using formslib)