Add "grouping" of snapshots by domain name

[bnvk]

Seems like it should be a relatively low-hanging fruit to offer filtering by archived snapshots that are "grouped" by domain name. Example, consider having the following memories:

- domain.com/article/4
- other-domain.com/some-page
- domain.com/article/3
- another-different-site.com
- domain.com/article/2
- other-domain.com/fist-page
- old-other-different-site.com
- domain.com/article/1

Then there could be a list of "domains" displayed which would display the following:

- domain.com (4)
- other-domain.com (2)
- another-different-site.com (1)
- old-other-different-site.com (1)

The numbers on the right would be the number of URLs indexed for that domain. Additionally user can then click on a given domain to display only snapshots.