AppIndicator Support for OpenPGP Applet

Since upgrading to Ubuntu 17.10 I am no longer able to use the OpenPGP Applet.

From what I've been informed supporting AppIndicator should be simple or is the issue deeper than this?

https://github.com/ubuntu/gnome-shell-extension-appindicator/issues/105#issuecomment-341136565

Copied from Tails bug tracker #14925