Optimize Spatial Queries

[p-a-s-c-a-l]

When the spatial index (table geom_search) of the Meta-Data Repository (PostgreSQL + PostGIS) is growing (e.g. new SHP resources are added, see #44), search for resources can become slow.

In addition to the optimisations already implemented in #46 try to rewrite / optimize SQL queries, improving indexing to match read patterns or investigate other measures for performace improvement (e.g. upgrade PostgGIS and gdal).