Dapp connection browser fox badge

## Background
We want to make it easily identifiable when an account is connected to a dapp by indicating a green dot badge on the MM browser extension fox icon. We should provide a 128x128 icon with a connection on/off option to be used during installation and by Chrome and Firefox stores. Extensions should also provide a 48x48 icon, which is used in the extensions management page (chrome://extensions). You can also specify a 16x16 icon to be used as the favicon for an extension's.

## User Story
As a user I want to see a green dot badge on the MM browser extension fox when I'm connected to a site

- The green dot should be visible when the selected account is connected with the site
- If the account is unselected or another account is active that's not connected to the site, the regular non-green dot icon should be used

## Designs
https://www.figma.com/file/aNEjTbMR6FsARVZBMbVNK4/Browser-fox-badge?node-id=0%3A84

Start with the linked Figma design and the browser extension icon configuration for the Chrome and Firefox stores, then trace how the selected account's connection to a site is represented. Done means the green-dot fox icon appears only for a connected selected account, while other account states use the regular icon and the required 128x128, 48x48, and 16x16 assets are provided.

Written by the indexing model from the issue text.