P: KBSC for "Back" in Lightroom Desktop

Tired of hunting down the "<back" for mouse click..

Instead just support the common browser keyboard combination "Alt + Left Arrow".

Discovery navigation in lightroom requires a lot of "back" navigation, like a browser does.

So just add the feature already built into modern browsers "Alt+ Left Arrow" goes to previous page.

This way users can quickly move to a page and pack.