Write Contest IDs on ballot for testing and review

[stratofax]

Add an option to the CLI interface to print the IDs below each candidate so we can proof them visually against the EDF itself, like this:

ballotmaker demo --show-ids

• @ion-oset Add contest IDs to each ballot measure selection (like "Yes" & "No")
• @cwulfman Create an EDF with human readable IDs (NIST-1500-100-103-examples #62: Use human readable identifiers for CVR and EDF elements)

[trustthevote]

good idea!

[stratofax]

@ion-oset Please review the single item checklist in the Issue description

[stratofax]

@trustthevote @ion-oset @cwulfman I've moved this issue under the new Pagination, page breaks, and page count Milestone. Ideally I'd like to use a new EDF with human-readable IDs, if it's available, to test this feature, to make it easier for the humans. Since this new milestone is #3 of 3, we don't need this updated EDF for a little while.

[stratofax]

Here's the related discussion: ion-oset/developer-commons#33