Popover: remove arrow, rounder, margins

[danirabbit]

[kurisubrooks]

I think my main point of contention is that if the arrow is removed, we need to signify that this popover is connected to X icon/panel item in another way.

Currently there's no active state for wingpanel items when a popover is open, so it just looks like another floating window with no relation to the content it opens from.

I also can't remember off the top of my head if we currently animate the popover contents, but adding a fade in + down animation to the popover would also help anchor the content to the panel item were the arrow removed.

[danirabbit]

@kurisubrooks animating the popover will take some more time, but how is it now with the checked state?

[kurisubrooks]

@kurisubrooks animating the popover will take some more time, but how is it now with the checked state?

I think the animation can be handled in a follow-up. With the :checked state, it should be sufficient for now. Did you want me to spin it off into an issue?

[kurisubrooks]

I'll create a follow-up issue for the animation, so this isn't blocked. Thanks 👍🏻

Edit: tracked in #705