Add ability for config file to define announcements.

[skyscooby]

Announcements are in limbo when it comes to declarative configuration..

Since vigil stores no state they are all lost on process restart or update. So every user needs to maintain a customise script to inject active notifications every time the service is restarted/updated or the system reboots.

It would be ideal to be able to define them in the configuration file to treat the service as configured through code

[valeriansaliou]

I intend to persist all Vigil in memory states whenever Vigil restarts in Vigil v2, which will fix that issue you report.