Implement a security repository service

[maccaf]

Add a security repository extension to allow third-party to provide customized implementation of security objects and storage.

Basic steps:

• Add an extension point.
• Add interfaces to access the repository.
• Add basic interfaces that security objects need to implement.
• Refactor the current security implementation with the new interface and move it to a new plugin.
• Refactor all places where the securities are loaded to use the new interfaces.