basichost: refactor to use DI for some services

[sukunrt]

1. Removes reference to Ping Service, and PeerstoreManager. They're started via the constructor.
2. Removes relay service manager. The relay service now deregisters the stream handler on reachability change.
3. Moves natmanager out of basichost. This now works similarly to ObservedAddrsManager.

This reduces the complexity in basichost and lets users opt into only the modules they're actually using.