PA Show page no longer loads geometry in to Rails

This would be just a normal performance tweak, but has become an
unfortunate necessity as previously selecting a PA with large (many
points) geometry would crash the Rails process due to RGeo/AR trying to
load it in to memory as an object.

Example -- WDPA ID 2898

This adds a `.without_geometry` scope to `SELECT` all attributes except
`the_geom`, and changes the PA bounding box calculation to use pure SQL
as once again, large geometries and RGeo just don't mix.
Limit number of database calls for PA bounds

Memoise the bounding box result (it'll never change)
Merge pull request #57 from unepwcmc/pa-without-geometries

PA Show page no longer loads geometry in to Rails