Clicking on the map will now show you the value

Clicking on the map will now show you the value under the cursor.
Uses AJAX to fetch value from a THREDDS WMS server.
Actual call to WMS server is done by django to allow cross-IP calls.

Only works with a THREDDS WMS server.
Made click to view value work with low longitudes

For longitudes under -180 degrees, climate analyser will now wrap
these values before making an ajax call.
Merge pull request #15 from Andrew-Dunn/legend

Added click to view value function for map