MDL-42666 repository_boxnet: Convert repository to APIv2
MDL-42666 repository_boxnet: Function to convert APIv1 references to true copies
MDL-42666 tool_boxnetapiv1migration: Admin tool to launch the migration
MDL-42666 repository_boxnet: Advise the user to run the migration tool
MDL-42666 repository_boxnet: Disabling file references
MDL-42666 repository_boxnet: Remove hardcoded date for APIv1 end of life