cylc 6 -  second db

Addresses #975

This change results in cylc creating two databases; one for the suite to query (the "primary") and one for external processes/utilities to query.

The "primary" database has it's permissions set so it is only accessible by the suite owner and is located in the 'state' directory. The external one is located in the suite root directory.

At present the two databases are identical but would become different once we re-work the data model in the "grand refactoring" with only utility relevant data being stored in the external database. At the moment, the main benefit is that suite processes will be the only things accessing the primary database while suite-state and rose-bush will access the external. This will further reduce the chances of writer starvation.