refactor editor callbacks, ensure card/atom changes go through callbacks

[bantic]

Refactor and document the editor's lifecycle callbacks.

• Remove the on event-emitting construction in favor of registering callbacks by name
• Ensure changes to card payload trigger the appropriate callbacks
• Ensure changing card display state triggers callbacks
• deprecate on('update') (aka didUpdate) callback (in favor of didRender)
• do not run callbacks after editor is destroyed