Show list of websites linked to each mask and allow removing sites from said list

[X-m7]

For users with the 5 mask limit, it would likely be inevitable that at least one of the masks would be used for more than one website. Currently, each mask only has one website clearly associated with it, but Firefox Relay evidently knows which sites are associated with which masks since it can show which mask I picked last time on each website's login page already, so exposing that list to users would be great.

Also, being able to remove sites from being associated with each mask (for example if I picked a mask but changed my mind and decide to use my real email address) instead would be great to keep things clean.