Improve the geosearch

Multiple things can / should be done to improve the geosearch:

• Currently, we need to Deserialize the whole RTree in memory before being able to do anything. This consumes a lot of RAM and thus is quite slow. => We should patch rstar to add the possibility to parse the RTree part by part
• When creating an RTree for the first time we should use the function bulk_load
• Add the possibility to sort the position by descending order. It will also require to modify rstar