This commit moves the routes lookup functions to be subcommands of
Machine, making them a lot simpler and more specific/composable.
It also moves the register command from cli.go into machine, so we can
clear out the extra file.
Finally a toProto function has been added to convert between the machine
database model and the proto/rpc model.
This commit rewrites the `routes list` command to use ptables to present
a slightly nicer list, including a new field if the route is enabled or
not (which is quite useful).
In addition, it reworks the enable command to support enabling multiple
routes (not only one route as per removed TODO). This allows users to
actually take advantage of exit-nodes and subnet relays.
This commit removes most of the locks in the PollingMap handler as there
was combinations that caused deadlocks. Instead of doing a plain map and
doing the locking ourselves, we use sync.Map which handles it for us.
