New secrets format based on Config::General for named connections.

[fozzmoo]

This is a rework of a previous attempt to create readonly database handles. While the previous work provided for backwards compatibility for the current secrets file format, this does not. There is now new code in freeside-upgrade that migrates from the old format to the new Config::General-based format.

[freeside]

For reference:

Please see: #17 (comment)

[freeside]

No general technical issues with this change, but this is a significant plumbing change without any actual usage in the application itself.

To merge into the open-source project (and thus ask everyone else to carry the maintenance and migration cost), we'd ask that you share a more complete change including the code changes which enable you to use read-only slaves effectively.

t doesn't seem very fair of us to merge just the low-level ability to connect to different databases into master without also including the code to make useful use of it.