add optional /geo suffix to /pollingstations
add optional /geo suffix to /pollingstations

for consistency with /councils endpoint.

/api/pollingstations.json and
/api/pollingstations/geo.json
do the same thing

chris48s/UK-Polling-Stations,DemocracyClub/UK-Polling-Stations,DemocracyClub/UK-Polling-Stations,DemocracyClub/UK-Polling-Stations,chris48s/UK-Polling-Stations,chris48s/UK-Polling-Stations