[Feature Request] Scope based buttons

Can you add ability to limit buttons visibility based on scope ex. text.md could then have buttons specific to markdown editing, but the same buttons are not required when editing cpp or other file types.
If undefined button should be visible in all scopes - that way you don't introduce BC and hard requirement on scope definition.

Re-posting this from: https://github.com/varemenos/atom-toolbar-almighty/issues/24

The issue names no files or tests. Start by locating where toolbar buttons are configured and where their visibility is decided, then inspect how Atom scopes are available there. Done means buttons can be limited to selected scopes while buttons without a scope remain visible everywhere, with coverage for both behaviors.

Written by the indexing model from the issue text.