Widget options in popup

[ablanathtanalba]

Fixes #2688.

This draft PR has bootstrapped the initial stepping stones for putting a section in the popup for replaced widget information, but there are some outlying questions:

• Should the section contained in the "dropdown" portion of the popup widget section have any more information than just the two "allow once" and "always allow" buttons?
• Should the popup widget section only show when the privacy badger placeholder has temporarily prevented the embed from loading, as in, should the popup section disappear when the user clicks through to allow the embedded media to load?
• In the less likely case that there are multiple widgets on a page, how should the section handle that?

I've attached the mockup here that I've been working with, there might be some questions about designing it better so that the sections are more logically related to themselves (maybe a slightly darker grey background on any expanded section in the popup?)

Also, the commit history here is a little janky, but that's mostly cuz of this branch working off the yet-to-be-merged #2748 PR that adds the firstparty scripts section and hides sliders by default. When that gets settled I'll come back here and cherrypick my way into a neater commit line.

[ghostwords]

Looks good!

We should probably list the widget names, so that you know which widgets we think have been replaced on this page, and so that you could selectively allow them.

Some *widgets* may have been replaced    >

And then clicking on the header gives you:

Some *widgets* may have been replaced    v

  [ ] Vimeo
  [ ] YouTube

  [ Allow once ] [ Always allow on this site ]

Clicking either button should update each checked item by disabling or removing the checkbox and showing a status message, something like "allowed" in green, maybe (like the error report sent successfully status message):

Some *widgets* may have been replaced    v

  [ ] Vimeo
  [x] YouTube   allowed

  [ Allow once ] [ Always allow on this site ]

What do you think?