In this commit, we extend the TorDial function and add a new attribute
to the TorProxyNet struct to allow the caller to opt for stream
isolation or not. Using stream isolation, we ensure that each new
connection uses a distinct circuit.
This commit adds the `lnnet` package which contains an
implementation of the newly created LightningNet interface which
multiplexes the Dial and DNS-related functions to use net
by default and torsvc if a flag is specified. This modularization
makes for cleaner code.