Add functionality for advanced control over peer set

I'd really like to have the ability to specify peer IDs in my config file that my node will try to always remain connected to. Additionally, it would be nice to specify strategies for these peers, like "always", which attempts to reconnect on any disconnect (respecting backoff rules), "preferred" which never closed a connection to that peer, but doesnt necessarily try and hold open a connection, and maybe one more that just increases the likelihood the conn manager will hold open the connection, but still allows it to be closed as needed.

This will enable me to keep connections open to friends machines, making transfers between us much more reliable.