Fix feedback penalty default value.

Currently, the production servers do not have the feedback penalty
column.  When this gets merged and deployed to production, the
records that have feedback_viewing_required must default the penalty
to 100.

- Add conditional default value for feedback penalty
- Hide the feedback penalty line item in the show view
  when the feedback need not be viewed
- When feedback penalty is not required, set the penalty value
  to 0 in Javascript to be consistent - since `null` value has
  an overloaded meaning.

[Finishes #77591162]

https://www.pivotaltracker.com/n/projects/1144352/stories/77591162