Import component marks from exam board files

Requires permission: ExamAdmin

Accepts whatever the board sent — JCQ a2c XML, a Cambridge International component marks spreadsheet, or a JCQ EDI results file — one file or several, and saves the marks against the given year. The format is detected from each file's contents, not its name. WorkbookMark chooses the raw, adjusted or weighted column of a spreadsheet; DuplicateHandling decides whether a mark that already exists is added alongside or overwritten; DryRun reports what would happen and writes nothing.