[#12547] Empty weights for MCQ

[peasantbird]

My experimental PR for CS3281! Targets Issue 12547

Outline of Solution

1. Allow weights to be null in validateQuestionDetails()
2. Update tooltip for "Options are weighted" checkbox
3. Show '-' for weighted percentages for options with empty weights
4. Update headers in per recipient statistics to show empty weights (denoted by Option[-])
5. Calculate correct total and average scores (skip over empty weights)
6. Show '-' for total and average when all options have empty weights

Screenshots

MCQ with empty weights can be saved:

MSQ with empty weights can be saved:

MCQ Feedback session results:

When all weights are empty:

With one or more non-empty weights:

MSQ Feedback session results:

When all weights are empty:

With one or more non-empty weights: