Add the option to have security classifications on plots

[ESadek-MO]

We've had a request for adding the option to have security classifications on Iris plots (OFFICAL, OFFICIAL-SENSITIVE, etc) in a way that is somewhat controlled and consistent.

We believe this could be possible as an optional parameter when creating a plot, but it wouldn't be realistic to automatically have it added due to external users. (In other words, you'd have to specify if you want a classification on your plot).

We think this should only be a small or medium effort issue to add, (days rather than weeks).

[ESadek-MO]

We think this would be best located in quickplot().
Potentially, if it fits comfortably, we could just make this the ability to add custom text to a plot.