Add `Empty Trash` button while in the trash folder (Issue #11)

Issue #11 (closed) MR !78 (merged)

It's a Draft because it doesn't look all that good and I would like to try something but I don't know how to do it (and couldn't find the solution by searching online). I want to see how it looks if the Box is styled like the location bar, shortcut pane, background of the main view. This flat "background" color + have an outline like they do. How can I do that? (the only relevant thing I found is gtk_set_style but there is only one call to this function in the entire codebase, so I gues that this isn't it)