GPX driver for H2 spatial

This PR introduces a GPX parser to import a GPX file into an H2 database.

The GPX parser is able to read formats 1.0 and 1.1. It uses the Java XML API and its based on the SAX event handler.

The syntax is
```sql
CALL GPXRead('/tmp/mygpx.gpx', 'tableName');
```

When a GPX file is parsed, many tables are created. It depends on the data contained in the file.
 
- `tableName_waypoint` stores all the `<wpt>` elements,
- `tableName_route` stores the `<rte>` elements. Each `<rte>` element is also decomposed into a 'tableName_routepoint that stores all the waypoints of an `<rte>`.
- `tableName_track` stores the `<trk>` elements. Each `<trk>` element is also decomposed into two tables: 
    * a `tableName_routesegment` that stores all segments (list of waypoints) of a `<trkseg>`,
    * a `tableName_routepoint` that stores all waypoints of each `<trk>` element.

For more about the GPX format, see here: http://www.topografix.com/gpx/1/1/