#840 Add import of psycopg2.extras so that we can get a dictionary output from the sql cursor.
This allows us to address fields within the list of results by name rather than index.
#840 Add methods to PostgresDBConnector to support the block_list checks.
#840 Update the DB interface so that it calls the get_list_of_blocks_* methods on the PostgresDBConnector instance rather than the MongoDBConnector instance.
#840 Slightly tweak the main app so that it can utilise the data now returned from Postgres rather than Mongo.
Convert .count(list) to len(list).
Merge branch 'feature/#840_Use_Postgres_to_retrieve_block_list' into develop