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.
Correct path to config.js in README.md
Merge pull request #41 from treekit/multi-city-support

Adding support for multiple cities
Fix typo in README path
Merge pull request #43 from jwalgran/topic/correct-config-js-path-in-readme

Correct path to config.js in README.md
Post the sql query as part of the form data, not the url.
- This is to avoid max url length problems.