Show all superdomains of identified tracking domains in the tracker list

[bcyphers]

When Privacy Badger identifies x.y.example.com as tracking, it adds the full domain as well as the TLD+1 to the action map, but not the TLD+2 (y.example.com). This is a problem for user control -- if a site performs all of its tracking under a TLD+2, but always from a TLD+3 domain, the user will have no way to set a slider for the TLD+2.

A simple fix could be to add an action map entry for every domain level recursively down to the TLD+1.

Related to #2259. This is a more specific problem that would be solved by #2259, but might be worth addressing on its own if #2259 is a wontfix.