Refactor audits and provide a helper for future fixing of #169
Add short descriptions to audits

Currently space is constrained on the plot detail page so we just show
the audit essentials. We may want to move this sort of logic to a
template at some point
Add method to get deleted tree ids on a given plot
Add recent edits to plot detail page
Merge pull request #170 from ahinz/topic/plot-audits

Topic/plot audits