Geojson exporter importer

This PR add two drivers to export a spatial table to a geojson format and import a geojson file to the database.
Supported standard is 1.0. Have look here to obtain more information http://geojson.org/geojson-spec.html.
Notes
1. currently the geojson parse does not take into account bounding box and crs. It will in the future. ;-)
2. the two drivers used the jackson library. So a new dependency has been added.


Syntax is 

To import 
```mysql

CALL GeojsonRead('/tmp/myfile.geojson','tableName');
```

To export 
```mysql

CALL GeojsonWrite('/tmp/myfile.geojson','tableName');
```