Finished test cases for answer consolidation within the API

Fixed parameter conversion to boolean

Make consolidate parameter case-insensitive

Increase verbosity of parameter name

ConsolidatedAnswerDistributionSerializer now a subclass of ProblemResponseAnswerDistributionSerializer

Implemented changes suggested in comments on open PR

Minor pep8 violation fixed

Responded to jbau's latest PR comment

Re-added missing import statement

Removed GET parameter for consolidation in favor of mandatory use, updated test cases

Moved non-consolidation logic out of initial loop to avoid returning partial set of data