MDL-47146 core_grades: fix class names

Class names for grade categories were the same as for the columns in the table causing errors
when selecting All/None items

Part of: MDL-46576
MDL-47146 core_grades: merge simple and full view in setup

Part of: MDL-46576
MDL-47146 core_grades: remove advanced mode in setup

Part of: MDL-46576
MDL-47146 core_grades: fix navigation bar in grades setup pages

Part of: MDL-46576
MDL-47146 core_grades: change action buttons on setup screen

Part of: MDL-46576
MDL-47146 core_grades: change columns on setup page

Part of: MDL-46576
MDL-47146 core_grades: Removed unused setup columns

Part of: MDL-46576
MDL-47146 core_grades: correcly align the select column

Part of: MDL-46576
MDL-47146 core_grades: Use a checkbox to override weights

Part of: MDL-46576
MDL-47146 core_grades: Improve labels of the fields on setup screen

Part of: MDL-46576
MDL-47146 core_grades: Behat test for Natural weights on setup screen

Part of: MDL-46576
MDL-47146 core_grades: improve navigation on grade pages

Part of: MDL-46576