MDL-9506 Renamed lib/gradebook to lib/grade (bug MDL-9506)

diff --git a/lib/gradebook/grade_calculation.php b/lib/grade/grade_calculation.php
similarity index 100%
rename from lib/gradebook/grade_calculation.php
rename to lib/grade/grade_calculation.php

diff --git a/lib/gradebook/grade_category.php b/lib/grade/grade_category.php
similarity index 100%
rename from lib/gradebook/grade_category.php
rename to lib/grade/grade_category.php

diff --git a/lib/gradebook/grade_item.php b/lib/grade/grade_item.php
similarity index 100%
rename from lib/gradebook/grade_item.php
rename to lib/grade/grade_item.php

diff --git a/lib/gradebook/grade_object.php b/lib/grade/grade_object.php
similarity index 100%
rename from lib/gradebook/grade_object.php
rename to lib/grade/grade_object.php