Simplified subpage header: add option to move hamburger menu

[laurelfulford]

Is your feature request related to a problem? Please describe.
Right now you can move the slide-out sidebar toggle to the left or right, but you can't do the same for the menu toggle when you use the simplified subpage header. This means you can have the toggle to the left or right on the homepage, but only to the right on subpages. This can result in a confusing mismatch of options.

Describe the solution you'd like
A second control to align the simplified subpage header left or right.

Describe alternatives you've considered
The toggle itself can be moved with CSS, but the amp-sidebar's position and animation comes from AMP, and is proving to be really difficult to override. So you end up with a confusing toggle-on-one-side-menu-on-the-other situation. Ideally, this would be done 'properly' so we can change the direction attribute of the sidebar correctly.