Allows for $0 options in extracosts.

Makes the Student Extra Costs module work with line item types that have
$0 options.

Adds a extra_costs_done Record to keep track of when a student has
completed the module.

Also adds a reset button for each group of radio buttons on the form.

Resolves Github Issue #1118.
Merge pull request #1128 from learning-unlimited/extra-costs-fix

Allows for $0 options in extracosts.