Minor improvements on PostgreSQL connection/operations

Currently, the database name (postgres) is hardcoded as well as the database user (ase) for accessing the data when creating the structure. These changes solve the issues step by step by first allowing the official PostgreSQL connection URI being passed, which allows to specify the database to connect to and then adding a new reset function which takes again a connection URI and a database user (which may have just enough permissions to access the db but not enough to create tables).