use locale dependent formatting, fixes #197

controllers/solutions.php

views/admin/edit_grades.php

views/exercises/cloze_exercise/edit.php

views/exercises/correct_exercise.php

views/exercises/courseware_block.php

views/exercises/lt_exercise/edit.php

views/exercises/print_exercise.php

views/exercises/tb_exercise/solve.php

views/sheets/edit_assignment.php

views/sheets/edit_exercise.php

views/sheets/list_assignments_stud.php

views/sheets/list_exercises.php

views/sheets/print_assignment.php

views/sheets/show_assignment.php

views/sheets/show_exercise.php

views/solutions/assignment_solutions.php

views/solutions/assignments_list.php

views/solutions/assignments_list_student.php

views/solutions/edit_solution.php

views/solutions/participants_overview.php