mail/oama: Update to 0.18

• Update the list of dependencies
• Pet port(clippy|fmt)
• Add pkg-message to be shown when the user updates the port from a version less than 0.15. That version had a breaking change.

Release changes:

https://github.com/pdobsan/oama/releases/tag/0.15
https://github.com/pdobsan/oama/releases/tag/0.16
https://github.com/pdobsan/oama/releases/tag/0.18

Reported by: portscout!