Feature/group stac features

[inigo-cobian]

Changelog:

• Make STAC endpoints readable from the collection URL instead of catalog URL + collection ID
• Add AWS reading capabilities (although not allowing its use yet)
• Reading geometry of collections from the same endpoint in static and API catalogs
• Navigate the STAC elements using the links instead of the relative paths
• Define a new order to get the assets (1st on the collection level, 2nd from item_assets, 3rd from a random query)
• Several bugfixes