Remove Audit.was_reviewed method

This method was created as part of an attempt to make a consistent API
for examining audit state. It ends up only being used in one place and
not adding much value. Taking it out.
Use a post_save signal for audit rep adjustments

This was probably an inaccuracy. There's no sane reason to apply an
audit reputation adjustment *before* the audit saves.
Expand ReputationMetric test coverage

Fixes #81 on github.

Add tests for different kinds of reputation adjustments.
Merge pull request #225 from steventlamb/topic/expand_rep_metric_tests

Topic/expand rep metric tests