Fix hardcoded assignment prefix "h..."

[alexstaeding]

The current MoodleUnpack file has a hardcoded format for the assignment id that begins with "h":

jagr/core/src/main/kotlin/org/sourcegrade/jagr/core/extra/MoodleUnpack.kt

Lines 42 to 46 in adb9022

	// TODO: Fix this hack
	val assignmentId = assignmentIdRegex.matchEntire(candidate.name)
	?.run { groups["assignmentId"]?.value }
	?.padStart(length = 2, padChar = '0')
	?.let { "h$it" }

Fix this so that other assignment id formats may be used (and may not necessarily be numbers)

[Atlasfreak]

bump