Feature Request: Custom MailConverter Actions

A bit like the way a developer can create and register Custom Workflow Functions, I have come across a use-case where it would be helpful to be able to register a Custom MailConverter Action that would perform a completely new process.

Currently the available actions are hardcoded in the Vtiger_MailScannerAction class and seem to be limited to one of three actiontypes: CREATE, LINK, UPDATE.