catching zero division erros in employer leaderboard
added query cache, performance optimization, fixed a participation % to account for multiple months
fixed issue when 'all' is specified as month
used prefetch_related instead of select_related to fix performance issue, changed survey cache to only query database once
exclude parent employer entry in checkin form
fixed unstyled bullet list on mobile
possible IE8 checkin map fix?
gerge branch 'dev' of https://github.com/greenstreetsinitiative/checkin into dev

Merge
fixe IE8 incompatiblities
Merge branch 'dev'