Push notification management is missing

[mattheworiordan]

We have a push section in the dashboards, yet we have no support in the CLI.

We need to add functionality to:

• Manage registrations, devices, subscriptions (CRUD)
• Send push notifications for testing

[mattheworiordan]

Resolved with #126, when it lands

[vladvelici]

Yesterday I added a push group and moved apps set-apns-p12 to it (I was working on this ticket). PR is here #125.

I see that you kept apps set-apns-p12. I think it's best if we just remove apps set-apns-p12 in #126 and close my PR?