Feature: Student ID number integration

[ngandrass]

• Add student ID number to quiz attempt header (fixes [Request]: Integrate student idnumber in quiz report metadata header table #49)
• Add student ID number to exported attempts_metadata.csv file inside quiz archives (fixes [Request]: Integrate student idnumber in quiz report metadata header table #49)
• Allow student ID number to be used in attempt filename pattern as ${idnumber} (fixes [Request]: Make idnumber a variable for filename pattern #33)
• Improve display of user firstname, lastname, and avatar in quiz attempt header
• Improve display of empty values in quiz attempt header (e.g., feedback, idnumber, ...)
• Fix single unit test suit execution command in developer documentation