Alignment button options (align to artboard)

This popover menu is currently "coming soon".

We'd like to have a checkbox (off by default) called "To Artboard" which makes the alignment of all selected layers work in relation to the artboard rather than their collective bounding box.

There has also been a request for letting the user choose a specific layer's bounding box to align all other layers to (meaning that chosen layer doesn't move, but the others do).

Potentially one more feature that would be handy is a way to choose between "deep" and "shallow" treatment of nested layers, where only the selected folders get aligned vs. each of their contents get aligned.