Total Coverage on Measure View

Story: https://www.pivotaltracker.com/story/show/61762256

Added simple total coverage percentage in aggregate results section of the individual measure view.

Current styling is a simple header-5 with a percent, dropped below the aggregate results views.

Current computation:
- iterate over the data criteria associated with the given measure
- store all of its keys in the <code>rationaleCoverage</code> hash
- iterate over each results' <code>rationale</code> hash
  - for each entry in the <code>rationale</code> hash, if it is truthy, then record a true value in the <code>rationaleCoverage</code> hash, otherwise if it is falsey and has not been marked true yet, then mark it as false
- the percentage is a simple computation of # of true values in the <code>rationaleCoverage</code> hash over the total number of values, rounded to a whole percentage