[etwist] fix bug w/ new resources concantenation and https-url enabled sites

oops

adds support for a portable db import/export format (closes: #1521112) the db-dump and db-restore cwctl commands are enhanced with a --format option (defaults to 'native'). If the format is 'portable', then the system database dump / restore is performed using pure SQL queries and the storage uses picked Python objects in a zip archive.