cf umap-project/Leaflet.Storage/commit/59583db7bef28b2fd13ac98c0a62e1a770d3fb66

- UMAP_MAPS_PER_PAGE
- UMAP_MAPS_PER_PAGE_OWNER

- This setting will exclude default maps (maps where the default center
  has not been updated)
- until now, the default was to exclude default maps - new default: not
  exclude

This also replaced pg_index with a simple builting seach
based on tsvector, as pg_index is not compliant with Django 1.8,
and as some old dependencies that would need to be upgrade too.