Add option to exlude navigation and/or status bar

Hey,

I think it would be nice if there was an option to exclude the navigation bar, since this part of the screen is almost always obsolete and not relevant for the screenshot.
Maybe a similar option for the status bar could make sense, too. Not as useless as the navigation bar, but also not always that relevant :)

Start by locating the Android screenshot creation and cropping flow, then determine where user-facing capture options are configured. Confirm how navigation and status bars appear in the resulting image, and define done as independently excluding either bar or both from screenshots.

Written by the indexing model from the issue text.