Adding support for multiple cities

These changes let TreeKIT Staff to config the map bounding box & species table
to be used from a CartoDB table called survey_areas. Configs are retrieved from
CartoDB taking into account the window.location.host + window.location.search
URL (ie: app.treekit.org?loc=hk, etc). By default, it will load NYC data.
Merge pull request #41 from treekit/multi-city-support

Adding support for multiple cities