[3.x] Form view sidebar control

[kallefrombosnia]

Summary

Currently, we don't have much control over the form sidebar. In the last 2.9.0 version, we were introduced to a getSubmitOptions method which returns custom action on specific states of the record.

Describe the solution you'd like

Like $indexOptions currently control the index view, I would like to see something like this on the edit forms.
We can control the switch button (draft/ live) per CMS user etc. This also can be implemented with getters and setters in a OO way.

[ifox]

@kallefrombosnia I'll move this to a discussion as it isn't clear which feature you're looking to add, and maybe what we added in Twill 3 covered it. Either way, open to discussion, but cleaning up our issues so we can focus our attention on addressing remaining bugs.