Format Requirement Numbers correctly on Challenge Create & Scorecard

[bryceglass]

Requirements in the requirements builder are currently appearing as 'requirement: 29' or some other randomly-starting sequence. Instead, let's implement recommendations from #299:

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Okay, after talking with @westonian this is what we'd like to display on the Challenge Creation side:

and here's how the same would appear on the Scorecard UI:

[gaitonde]

@bryceglass @westonian - fixed and pushed.

[westonian]

looks good on reqs list