It is unusal to use a hack to close overlays when there is a method
to do it.
This fixes a bug where user is unable to scroll message feed
after opening an overlay and then using browser back button.
This could have easily cause other bugs too.
When overlay / modal is displayed, scrollbar is hidden due to
the disabled scrolling on `html`. Reduce width of fixed elements
that will be visible in background and `html` so that they don't
occupy that extra space.
Also, I was over-thinking how we can get the scrollbar width. The
moment we allowed scrolling on `html`, it was easy to get the
scrollbar width.
Refactored some code as well to avoid unneccesaary `undefined`
checks in `overlays`. To be exact created an action_overlay
object of type `Overlay` such that the `reset_state` is just
`action_overlay = undefined` and having attributes like `$element`
and `close_handler`.
This would ensure that if you have an `active_overlay`, there will
be a registered `close handler` attached to it without needing to
write additional checks for `close_handler` just to satisfy type
checker.
Aman Agrawal
Alex Vandiver
Anders Kaseorg
Lalit