New section under "User Statistics" about rock-and-pebble "geneology" data

[DanielEFrampton]

As a registered Paired user,
When I login,
And I click the user dropdown menu,
And I click "View Stats,"
Then I see a section or sections about rock & pebble stats, such as:

• How long the longest chain of rock & pebbles I belong to is (e.g., my rock has a rock, and I have a pebble, so this number is 4.)
• How many pebbles I have had, both active and inactive

(Copied from Rock & Pebble project board, was left on the dream pile)